I Interpretation of the Composition and a i Classification of P the Chlorites

GEOLOGICAL SURVEY PROFESSIONAL PAPER 414-A Interpretation of the Composition and a Classification of the Chlorites

By MARGARET D. FOSTER

SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY

GEOLOGICAL SURVEY PROFESSIONAL PAPER 414-A

A study of the compositional relations of chlorites and a classification based on the two principal types of ionic replacement found in them

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1962 UNITED STATES DEPARTMENT OF THE INTERIOR STEWART L. UDALL, Secretary

GEOLOGICAL SURVEY Thomas B. Nolan, Director

For sale by the Superintendent of Documents, U.S. Government Printing Office Washington 25, D.C. CONTENTS

Page Page Abstract ______A-l Si and R+a replacement of R+8 ____.__.___.__ A-13 Introduction ___..._.____... 1 Fe+s replacement of Al and R+2.______.____. 14 Selection of analyses ___.___ 2 Status of Fe203 in chlorites __..___ __ .__ 15 Structural formulas ...... __.__ 2 Classification of chlorites.______17 Calculation of formulas._____.__..._.._._._. 2 Some previous classifications ___.__._._ 17 Theoretical 0(OH) versus determined HsO ( + ).__ 3 Classification based on ionic replacements.._... 17 Relation between Fe*8 and 0 ..._-__..._._ ._ _-_ 5 Relation between tetrahedral and octahedral Al...__._ 7 Allocation of octahedral cations...______..._.... 22 Relation between Si and Fe+2 :R+2____.._.__._._.._._ 11 Summary and conclusions..___.______. 24 Magnesium replacement series__.....___..__._ . _ 12 References cited ______25

ILLUSTRATIONS

Page FIGURE 1. Relation between Fe+s and 0 in chlorites-______A-6 2. Relation between tetrahedral Al and octahedral Al__._..___.__.____...... _.._ _ 8 3. Relation between octahedral occupancy and octahedral R+s (and R+4) cations in excess of tetrahedral R+s cations...__ ._.____._____._..____.___._ 10 4. Relation between formula positions occupied by Si and the Fe+a :R+z ratio.._.. .._..._.._... 11 5. Diagrams of octahedral groups of average formulas showing transition in character from highly magnesian to highly ferroan in the Si range 2.50-2.70 _. ._.._. 12 6. Diagrams of average formulas showing change in composition of chlorites having Fe+2 :R+2 ratio less than 0.10 with increase in Si content _ __ _.. 14 7. Diagram showing relation between Fe+a :R+2 ratio and Fe20s in chlorites.__._...._.___._ 16 8. Classification of chlorites studied according to Hey (1954) ._.______. 18 9. Classification of chlorites based on the two principal types of ionic replacement ...... _.. 19

TABLES

Page TABLE Example of the calculation of structural formula of chlorites _ A-3 Analyses and data for writing formulas of chlorites used in study- 27

III

SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY

INTERPRETATION OF THE COMPOSITION AND A CLASSIFICATION OF THE CHLORITES

By MARGARET D. FOSTER

ABSTRACT octahedral ions present is most likely, but that the way the Structural formulas calculated for more than 150 selected ions are distributed may not necessarily be the same in all published analyses of chlorites show that octahedral Al is chlorites. not often closely equivalent to tetrahedral Al, being higher in INTRODUCTION about one-fourth of the formulas, and lower in about one-half. If lower, some other octahedral trivalent cation, usually Fe+a, The chlorites are hydrous silicates of aluminum, is present and proxies for Al in providing sufficient octahedral and magnesium and (or) ferrous iron; many contain positive charge to balance the tetrahedral negative charge. ferric iron, and some contain chromium or man­ Octahedral occupancy is close to 6.00 only if the sum of the ganese. The chlorites vary greatly in chemical com­ octahedral trivalent cations is approximately equal to tetra­ hedral Al. If it is greater, as is most usual, octahedral occu­ position, and this great variation led in the past pancy is less than 6.00 formula positions by an amount equal to the introduction of many varietal names, some to about one-half the excess of octahedral trivalent cations without adequate definition. Some names have been over tetrahedral Al, indicating that the excess octahedral used to indicate a certain range in composition, but trivalent cations replace bivalent cations in the ratio of 2:3. there is considerable overlapping, and the limits of No correlation was found between Fe20s and 0 content in excess of 10.0 ions per half cell. This, and the facts that in ranges of composition have been fixed arbitrarily and many chlorites some or all of the Fe+3 present is necessary for variously by different investigators. Before X-ray structural balance, and that many chlorites are formed as methods of study were available, various attempts alteration products of other minerals that may contain Fe+8 were made to classify the chlorites. In most of these ions, suggest that Fe20s is a normal constituent of many classifications, as, for example, in that of Tschermak chlorites, particularly of ferroan chlorites, and that its pres­ (1891), Orcel (1926), Winchell (1936), and Halli- ence should not arbitrarily be taken as evidence of secondary oxidation. mond (1939), the composition of chlorites was inter­ Two series of ionic replacements characterize the chlorites, preted as made up of varying proportions of certain replacement of tetrahedral and octahedral Al by Si and Mg, end members. Since Mauguin's pioneering work and replacement of Mg by Fe+2. Replacement of one Al(IV) (1928, 1930) in elucidating the chlorite structure, and one Al(VI) by one Si and one Mg involves both the tetra­ X-ray studies have shown that all members of the hedral and octahedral layers and causes changes in the layer charges, but replacement of one Mg by one Fe+2 involves only chlorite family have the same type of structure and the octahedral layers and does not change the layer charges. that the compositional differences of chlorites can Replacement of Al(IV) and Al(VI) by Si and Mg amounts to be attributed to isomorphous replacement of cations about one formula position in the group of chlorites studied, within the structural framework, as in the micas. from about (AU.aoMg4.4o) (Si2.4oAl1.eo)Oio(OH) 8 to about (A1.60 Such investigations have also shown that several MgB.«.)(Sis.4oA1.6o)01o(OH) 8, and is represented most fully by species formerly included with the group, such as the highly magnesian chlorites. The replacement of Mg by Fe+2 is demonstrated most continuously and completely by amesite (Gruner, 1944) and cronstedtite (Hen- chlorites in the lower part of the Si range, Si 2.50-2.75, where dricks, 1939) do not have the chlorite structure. the full range, from wholly magnesian to wholly ferroan is Faust (1955) provided the X-ray proof that removes represented. griffithite from the chlorite group. A classification scheme for the chlorites, based on these two Pauling (1930) showed that the composition replacement series, divides the chlorites into nine species of the chlorites requires that in one unit length which are strictly defined on the basis of Si content and along c there be two layers of Si-0 tetrahedra and ratio of Fe+2 to R+2. After consideration of various ways of distributing the two octahedral layers, similar to brucite, Mg(OH) 2, octahedral cations between the two octahedral layers, it is with one of the octahedral layers bound between the concluded that an equal distribution of the various kinds of two tetrahedral layers, forming a micalike unit. A-l A-2 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY With micalike units and brucitelike layers alternat­ of analysis as, for example, determination of fer­ ing, there is thus also alternation of tetrahedral and rous iron or incompleteness in analyses. Next, all octahedral layers. The structure leads to the general analyses later than 1900 in which more than 0.5 formula XmY4Oi0 (OH) 8, with the tetrahedral layers percent of Na20, K20, or CaO were reported were having the formula Xm/2Y4Oio(OH)2, and the octa­ excluded. There is no place in the chlorite structure hedral layers having the formula Xm/2 (OH) 6. In for cations as large as Na+, K+, and Ca+2, and their these formulas X and Y represent octahedral and presence suggests interlayering or admixture with tetrahedral cations, respectively, and m is usually 6, mica and (or) montmorillonite, or the presence of or somewhat less, but not more. If Y were made up associated carbonates or silicates. In this connection, entirely of 4 Si+4 ions the tetrahedral layers would the high alkali content in chlorite analyses reported be neutral, as 16 of the 28 negative charges carried by Polovinkina and Ivanova (1953) may be cited. by Oio(OH) 8 are associated with the tetrahedral The surprisingly high alkali content reported in layers; but in all chlorites there are some R+3 ions, these analyses, as much as 4.5 percent, is attrib­ usually Al+3, proxying for Si+4, and the tetrahedral uted by the authors to intergrown relict mica. This layers have a resultant negative charge equivalent amount of alkali indicates that a considerable pro­ to the amount of Al+3 proxying for Si+4. Similarly, portion of the analyzed sample was mica, conse­ if X were made up entirely of 6 R+2 ions, the octa­ quently the analyses cannot be relied on as indicative hedral layers would be neutral, as the 12 positive of the composition of the chlorite present. As the charges carried by 6 R+2 ions would just neutralize relation of trivalent to bivalent octahedral cations the 12 negative charges associated with the octa­ is of particular interest in this study, all analyses hedral layers. However, for structural balance the that did not report both Fe203 and FeO were also octahedral layers must carry a positive charge equiv­ discarded. alent to the negative charge on the tetrahedral layers, Finally, analyses in which the amount of H20 and consequently, the octahedral layers must contain reported was significantly low (less than 9.5 per­ R+3 cations sufficient to balance the negative tetra­ cent) or significantly high (more than 13.5 percent) hedral charge. were excluded. Some variation in H20 content is, of The presence of layers not held together by anion- course, to be expected. Chlorites that have a high cation contacts explains the excellent cleavage on ferric-iron content, especially, may have a lower (001). The cleavage lamellae, though tough, are not than normal H20 content. But even so, analyses so elastic as those in the micas, as the effect of the reporting less than 9.5 percent H20 are highly sus­ K ions in keying adjacent layers is absent in the pect. No reason such as reduction, as opposed to chlorites. On the other hand, the chlorites, because oxidation, can be asserted to account for high water of the presence of alternately negatively and posi­ content. Analyses reporting significantly high water tively charged layers, are not as soft as kaolinite and are suspect as indicating an inaccurate water deter­ talc, whose layers are not charged. mination or the presence of contaminants, like mont­ In the present study, which is based on formulas morillonite, that are characterized by high H20 calculated from more than 150 published analyses, content. attention is given to the principal types of ionic STRUCTURAL FORMULAS replacement in the chlorites, the effect of R+3 proxy­ ing for R+2 on octahedral occupancy and layer charge CALCULATION OF FORMULAS relations, and the status of Fe+3 in chlorites. A clas­ Structural formulas for all the analyses given in sification scheme based on the principal types of table 2 were calculated on the basis of the theoretical replacement is proposed. 0(OH) content of the unit cell of chlorite, 020 (OH) 16. For comparative purposes a second set of formulas SELECTION OF ANALYSES were calculated on the basis of determined H20(+) About 150 analyses of chlorites were selected from for those analyses in which H20(+) and H20( ) the literature for study. These analyses are given in were both reported. table 2. In selecting analyses for study, all analyses The method used in calculating formulas on the published before 1900 were excluded. This restric­ basis of the theoretical 0(OH) content was adapted tion inevitably excludes some good analyses, but it from the method used for calculating the formulas also eliminates a large number that are unreliable of micas (Foster, 1960) by using the number 56 or unsatisfactory, either because of failure to purify instead of 44 (for the mica) to convert gram equiva­ the analyzed sample properly, inaccurate methods lents of cationic constituents to cationic valences per INTERPRETATION OF THE COMPOSITION AND A CLASSIFICATION OF THE CHLORITES

TABLE 1. Example of calculation of the structural formula of a chlorite

Gram-equivalent Cationic Cations Cations of cationic valences per per per Percent constituents unit cell unit cell half cell SiOi ____-30.44 -4- ( 60.04 -r- 4) = 2.027 -T- 0.0881 = 23.008 * 4 = 5.752 2.88 ^ 2.248 1.12 8.000 4.00

Al2Os _.__.__ 18.13 -f- (101.96 -r- 6) = 1.066 -j- .0881 = 12.100 ^3 = 4.033- » 1.785 .89 "1 I 1.13 R+3 Fe203 -- 3.38 -~ (159.70 -r- 6) = .127 -r- .0881 = 1.441 -=- 3 = .480 .24 j ions

FeO-__--__- 0.57 -f- ( 71.85 -r- 2) = .016 -r- .0881 = .182 -r- 2 = .091 .05"] I 4.87 R+2 MgO___--34.22 + ( 40.32 ~ 2) = 1.697 -T- .0881 = 19.262 -r- 2 = 9.631 4.82 I ions 4.993 55.993 11.987 6.00

4.993 -f- 56 = 0.0881 H2O---____ 0.30 HtO+_____12.70 + (18.016 -=- 2) = 1.409 -T- .0881 = 16.016 -f- 1 = 16.016 8.01 6.342 72.009

6.342 -f- 72 = 0.0881 O = 18 - 8.01 = 9.99 Structural formula (half cell)

unit cell. The calculations involved are illustrated The aluminum ions are divided between the tetra- in the example shown in table 1. The gram equiva­ hedral and octahedral groups; enough Al is allocated lents of cationic constituents in the structure are to the tetrahedral group to bring the total number obtained by dividing the percent of each constituent of cations in that group, with silicon, to 8.00, and reported in the analysis by a factor obtained by the remainder is assigned to the octahedral group dividing the molecular weight of that constituent by with the other cations. This assignment of Al ions the number of cationic valences in its molecular to fill the tetrahedral group is in accordance with formula. Thus, for F^Os the factor to be used is the customary procedure, and does not preclude the molecular weight of Fe203, 159.70, divided by 6, possibility that other trivalent cations, Fe+3 or Cr43, which is 26.617; for FeO it is 71.85 divided by 2, may not occupy such sites in certain chlorites. The or 35.925. sum of the octahedral cations, theoretically, should The second step in the calculation is to convert be 12.00, 6.00 in each of the octahedral layers, but gram equivalents of cationic constituents to cationic in many of the calculated formulas for chlorites it valences in the unit cell. The number of cationic is less. valences must equal the number of anionic valences, Most of the discussion in this report on character­ which, theoretically, is 56, as each of the 20 0 ions istics of the chlorites is based on the half-cell for­ in the unit cell carries two negative charges and mulas. To write the half cell formula the values for each of the 16 OH ions carries one. The sum of the the cations in the unit cell are merely halved, as in gram equivalents of the cationic constituents was, the formula at the bottom of table 1. therefore, divided by 56 to obtain the factor for con­ THEORETICAL O(OH) VERSUS DETERMINED H2O(+) verting the gram equivalents of each constituent to the number of cationic valences in the unit cell. After Theoretically a chlorite contains no "adsorbed" dividing the gram equivalents of each constituent water, H20( ); all the water present is "hydroxyl" by this factor, the number of valences thus obtained water, H20 (-]-), and the figure given in the analyses for each cation is then divided by its valence to for total water may thus be used in calculating the obtain the number of cations of that species in the formula. However, very few of the analyses in which unit cell. H20(-j-) and H20( ) were differentiated report 0.00 A-4 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY percent H20 ( ). Most of them report some H20 ( ), lated on the basis of theoretical 0 (OH), as shown be­ the amounts ranging from a few tenths to almost low in the pair of formulas for analysis 126, table 2. 2 percent. In view of this, formulas based on deter­ In the first pair of formulas there is considerable mined H20(+) were calculated only for those analy­ excess of (OH) and deficiency in 0 in the formula ses in which both H20(+) and H20( ) were re­ calculated on the basis of determined H20(-f) as ported. In calculating formulas for such analyses, compared with the theoretical 0(OH) content. The the value of H20(+) was included with the cationic decrease in the number of anionic charges present constituents, and the sum of the gram equivalents is reflected in the decreased number of cations pres­ of cationic constituents was divided by 72, (each of ent, 0.21. Magnesium occupied 0.09 fewer positions, the 36 oxygen in the unit cell carrying two negative Al(VI), 0.11; and Si 0.05. In the second pair of charges) instead of 56. formulas, the formula calculated on the basis of In the sample calculation shown in table 1, the determined H20(+) has considerable excess of 0 factor for converting gram equivalents of cationic and deficiency of H compared with the theoretical constituents to cationic valences per unit cell is the 0(OH) content. The increase in cationic charges same, 0.0881, whether the calculation is on the basis present is reflected in the greater number of cations of the theoretical 0(OH) content or determined present, 0.37. Mg occupies 0.07 more positions; Fe+2, H20(-f). This indicates that the determined figure 0.06; Fe+3, 0.03; Al(VI), 0.21; and Si, 0.11. for structural water is very close to the theoretical. The two examples above are near the extremes in Factors based on determined H20(-j-) that are variation in 0 and OH content found in the 65 for­ larger or smaller than those based on the theoretical mulas calculated on the basis of determined H20(+). O(OH) content indicate proportionate differences, The differences in the number of formula positions plus or minus, between the theoretical and the deter­ occupied by the various cations between formulas mined OH content. The greater the difference in fac­ calculated on the basis of determined H20(+) and tors the greater is the difference in the number of the number of positions occupied by the same cations structural positions occupied by the various cations in formulas calculated from the same analyses on the in the formulas based on the theoretical 0(OH) basis of the theoretical 0 (OH) content are not great content and on determined H20(+) values. enough to change the general character of the chlo- If the factor for converting gram equivalents to rites represented nor to change their classification, cationic valences per unit cell is greater when calcu­ unless they happen to be on the borderline between lated on the basis of determined H2O(+) than on species. In all the other analyses for which two the basis of theoretical 0(OH) content, the number formulas were calculated, the differences are less of cations of the various constituents in the half-cell than in the two examples cited. It can be concluded, formula calculated on that basis is less than that in therefore, that for a study of the general character­ the formula calculated on the basis of theoretical istics of chlorites as a group, formulas calculated on O(OH). This is illustrated in the following pair of the basis of the theoretical 0(OH) content are en­ formulas for analysis 12, table 2: tirely satisfactory.

Determined H20( + ), factor = 0.0907- ~_[Ali.u Fe£ Mg«.iB)(Sii.B Ali.«) 09.42

Theoretical 0(OH), factor = 0.0889.. ___[(Ali.« Pe^Mg^XSkn Ali.37)Oio(OH) 8]

If the reverse relationship applies, the number The temperatures at which H20( ) is usually of cations of the various constituents in the half- determined, 100° or 110°C, were fixed long before cell formula calculated on the basis of determined thermal analysis techniques were developed. Studies H20(+) is greater than that in the formula calcu- of chlorites by such techniques show that adsorbed

Determined H20( + ), factor = 0.0791._...... _-_[(Ali. ea Fe.+a38 Fe£o Mgi.M)(Si,.M Ali.ot)Oii.io(OH)a.»]

Theoretical 0(OH), factor = 0.0820 __. ____[(Ali.«, Fe& Fe& Mgi.w)(Sii.M Ali.i6)Oio(OH)s]

6.66 INTERPRETATION OF THE COMPOSITION AND A CLASSIFICATION OF THE CHLORITES A-5 water, H20( ), continues to be given off to temper­ The H20(-r) content reported in the analyses from atures as high as 500° C. Determination of H20( ) which these formulas were calculated is much lower at 100° or 110° C would tend, therefore, to give a low than can be accounted for by secondary oxidation of H20( ) value, and a high H20(-f-) value, and the Fe+2. The high octahedral occupancies obtained when factor for converting gram equivalents to cationic these H2O(-f-) values are used in calculating the valences per unit cell would be correspondingly high. formulas strongly suggest that the H20(+) values Low values for H20(-f-) and, consequently lower reported are in error, and do not represent the true factors than those based on the theoretical 0(OH) hydroxyl content of the samples. values, as illustrated in the second pair of formulas In formulas like these, in which the use of the above, may be due to oxidation of FeO to Fe203 dur­ determined H20(-f-) value yields an octahedral oc­ ing the H20(+) determination, in accordance with cupancy significantly greater than 6.00, the erro­ the reaction, 2Fe(OH) 2=2FeO(OH) +H2. This re­ neous nature of the H20(-j-) value is obvious, but for action requires the conversion of one (OH) to O for chlorites in which the octahedral occupancy is con­ each ion of Fe+2 oxidized to Fe+3. siderably less than 6.00, a low H20(+) value might Low H20(-f-) values and low factors for convert­ still produce a formula in which octahedral occu­ ing gram-equivalents to cationic valences per unit pancy is no more than 6.00, and the possibility that cell could also be produced by secondary oxidation the H20(-f-) value is low is not so obvious. Nor does of FeO to Fe203 in place. Thus chlorites that have a high value for H20(-f-) produce a formula that is undergone secondary oxidation should be character­ obviously suspect. A high value for H20(-f-) yields ized by a low H20(+) value and by a low conversion a conversion factor that is higher than that obtained factor as compared with the theoretical. Such low on the basis of the theoretical 0(OH) content. Con­ values for H20 (-f) would be more to be expected in sequently the number of octahedral cations is lower chlorites containing considerable Fe203, like the than that obtained if the factor based on the theo­ chlorite represented by the second pair of formulas retical 0(OH) content is used. If both are 6.00 or above, which contains 8.33 percent Fe203. In some less, there is no reason for suspecting the deter­ analyses, however, the H20(+) content and the mined H20(-f-) value, unless there is considerable conversion factor used in calculating the formulas discrepancy between the two values, for which no on the basis of determined H20(-f) is so low that reasonable explanation can be advanced, such as the octahedral occupancy is considerably greater secondary oxidation of Fe+2. than 6.00, whereas formulas calculated on the basis of the theoretical 0(OH) content have octahedral RELATION BETWEEN Fe+3 AND O occupancies of 6.00 or less, as in the following By regarding the Fe203 in chlorites as the result examples: of secondary oxidation of FeO, Winehell (1926) was Analysis 1, table 2 (Fe2O3=3.42 percent), Fe.+£ Fe % Mg3.8 ) (Si2.B

.36 Ti.oi Fe S Fe S i2.tt Ali.») 010(OH)8]

Analysis 33, table 5 (Fe203=0.83 percent), li.44 Fe.tS Fe £ Mg^) (Si,.w Aim) Oio.86(OH)r.i4]

+£ Fe $ Mg«.») (Si2.so Al1.So)Olo(OH) 8]

Analysis 133, table 2 (Fe203=2.81 percent), li.« Ti.o2 Fe S Fe&Mg,.io) (Si..* Al.n)On. w(OH)6.»]

[(Ali.M Ti.o2 Fe £ Fe&Mg,.*) (Si..« A-6 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY

EXPLAIMATION / K 11.2 0 content theoretical

11.0 /

( t

9 10.8 /

LU z> - _J &/ > + 10.6 * O CM I » /

CD / S 10.4 */ B ' i o * z. i i /

% 10.2 A c/> * * /

1 ' O /

10.0 ®X X *> x x x x x x c xx X X xxx X

9.8 X X x X 5 x x ( X 9.6 x

X 9.4 O.C)0 0.20 0.40 0.60 0.80 1.00 1.20 1.40 OCTAHEDRAL POSITIONS OCCUPIED BY Fe+3 2.5 5.0 7.5 10.0 12.5 15.0 17.5 APPROXIMATE CONTENT OF Fe203, IN PERCENT

FIGURE 1. Relation between Fe-^8 and O in chlorites. INTERPRETATION OF THE COMPOSITION AND A CLASSIFICATION OF THE CHLORITES A-7 able to reduce some leptochlorites to orthochlorite composition, but others could not be reduced to ortho­ [Ali.oo(Fe? Mg) 5.oo](Sis.oo Al1.0o)Oio(OH)8 chlorite composition in this way. Following Winchell, Holzner (1938) also showed that many analyses of leptochlorites are reduced to orthochlorite composi­ +0.60 -0.50 [Al.6o(Fe +,2 Mg) 5.6o] (Sis.BO Al.BO)Oio(OH)8 tion when all the Fe203 is reduced to FeO. He ex­ plained the secondary oxidation of Fe+2 to Fe+3 in terms of the following reaction, Thus, theoretically, octahedral Al should be equiva­ 2Fe(OH) 2 - 2FeO(OH)+Ha lent to tetrahedral Al. However, in most formulas This reaction requires the conversion of one OH calculated from analyses of chlorites, octahedral Al to 0 for each ion of Fe+2 oxidized to Fe+3. Thus chlo- is either greater or less than tetrahedral Al. The rites that have undergone secondary oxidation should relation between tetrahedral and octahedral Al in be characterized by an 0 content greater that 10 ions the formulas calculated from the analyses in table 2 per half-cell by an amount equivalent to the Fe+s is shown in figure 2. In this figure the 1 : 1 relation present. between tetrahedral and octahedral Al is represented To study the relation between Fe+3 and 0 in chlo- by diagonal line A. In most of the chlorites repre­ rites, the number of positions occupied by Fe+3 was sented, octahedral Al is less than tetrahedral Al, plotted against the number of positions occupied by although some show a contrary relation; in rela­ 0 in formulas calculated from analyses reporting tively few is octahedral Al just equivalent to tetra­ both H20(+) and H20( ), as shown in figure 1. hedral Al. In some of the latter, Al may represent The approximate amount of Fe2O3 as reported in the the entire octahedral R+3 present, as in the following analyses is indicated below the number of formula formula for analysis 59, table 2, positions occupied by Fe+3. The hypothetical relation between Fe+3 and 0 in excess of the 10 oxygen ions Fe.+7l Mg^.31 Mn.+oi ) (Si,, oo Al1.oo)Oio(OH) 8]-0-0 in the half cell, according to the above equation, is indicated by the diagonal line A (fig. 1). The loca­ tion of most of the points indicates that there is little in others it may make up only part of the octahedral relation in these chlorites between Fe+3 and 0 cal­ R+3 present, as in this formula for analysis 123, culated from the H20(+) values given in the analy­ table 2, ses. A few points indicate an 0 content high with +1.16 -1.16 respect to Fe+3, and several points, some representing Fe 2+.!3 Mgl.82) (Sia.8i Ali.i8)Oio(OH) 8] 0-° chlorites containing considerable Fe+3, indicate an 0 content of less than 10. As has already been pointed out, determined H20(+) values tend to be high In the first of these formulas Al makes up all the rather than low because they include some H20( ) trivalent octahedral cation and is about equivalent water. The fact that 0 is low with respect to Fe+3 to tetrahedral Al, and octahedral occupancy is in most of the chlorites represented in figure 1 6.01, but in the second formula, octahedral Al is lends little support to the hypothesis of secondary equivalent to tetrahedral Al but makes up only oxidation. part of the R+3 octahedral cations, and octahedral occupancy is only 5.77, a deficiency of 0.23 positions. RELATION BETWEEN TETRAHEDRAL AND OCTAHEDRAL Al If Al were the only trivalent octahedral cation in this second formula, it may be assumed that, as in Substitution of Al+3, or other trivalent ion, for the first formula, octahedral occupancy would be Si+4 gives the tetrahedral layers a negative charge complete and that R+2 would occupy 4.84 positions. equivalent to the amount of R+3 proxying for Si+4. However, R+2 occupies only 4.15 positions, or 0.69 For structural balance the octahedral layers must position less, and Fe+3 occupies 0.46. It is evident, have a corresponding positive charge, and, conse­ therefore, that Fe+3 has replaced R+2 in the ratio of quently, must contain at least as many R+3 ions as 2:3, and that the 0.46 negative charge associated the tetrahedral layers, as illustrated in the following with the 0.23 unoccupied octahedral position neutral­ formulas: izes the 0.46 extra positive charge carried by Fe+3, +1.50 -1.60 as compared with the amount of charge that would [Ali.60(Fe +f have been carried by the same amount of a bivalent cation. A-8 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY

TS1

1.60

o: o 1.40 UJ

oH o

1.20 o UJ CL O O O 1.00 z o

0.80

cc O

0.60

0.40 0.60 0.80 1.00 1.20 1.40 1.60 1.80 FORMULA POSITIONS OCCUPIED BY TETRAHEDRAL Al

FIGURE 2. Relation between tetrahedral Al and octrahedral Al.

In chlorites represented by points falling above In the first formula, 1.40 of the extra charges car­ line A (fig. 2) octahedral Al is greater than tetra­ ried by Al form a positive charge on the octahedral hedral Al. In some of these chlorites Al is about the layers, neutralizing the negative tetrahedral charge. only trivalent octahedral cation present, as in these The rest of the Al, and all the Fe+3 (and Ti), occupy­ formulas calculated from analysis 101, table 2, ing 0.47 positions, may be interpreted as replacing

+1.40 -1.88 R+2 in the 2:3 ratio, with the 0.48 negative charge [(Ali.82 Ti.m Fe .+4 Fe^i Mg!.i3 Mn % ) (Si^ Ali.38)Oi0 (OH)8] +0 « associated with the 0.24 unoccupied octahedral posi­ tion neutralizing the extra 0.48 positive charge they carry. Similarly in the second formula, 1.34 Al pro­ and from analysis 17, table 2, vides the positive charge on the octahedral layers, +1.84 -1.84 with the rest of the Al and the Fe+3, 0.22, replacing [(Ali.54 Fe & Fe .+d Mg4.8o) (Si2.8a Al1.34)Oi0(OH)8] c R^2 in the 2:3 ratio. In other formulas in which octa­ hedral Al exceeds tetrahedral Al, other trivalent INTERPRETATION OF THE COMPOSITION AND A CLASSIFICATION OF THE CHLORITES A-9 cations are also present in significant amounts, as formulas octahedral Al is significantly lower than in the following formulas for analysis 148, table 2, tetrahedral Al, and Fe+3 may be interpreted here as

-1.81 replacing Al in a 1:1 ratio. That Fe+3 replaces Al [(Ali.«Pe£ Ji2.69 Ali.8i)Oio(OH)8]-0-0 in this ratio and does not replace R+2 in the 2:3 ratio is indicated by the octahedral occupancy, which is 6.00 or very nearly so. In some of the other chlorites and for analysis 128, table 2, represented by points below line A in figure 2, some

+1.12 -1.12 but not all of the Fe+3 is necessary to give the octa­ [(Ali.« Fe £ Fe & Mgi.w) (Si*.*, A hedral layers sufficient positive charge, as illustrated in these formulas for analysis 88, table 2, In these formulas, as in the two preceding, octa­ +1.45 -1.46 hedral R+3 in excess of that necessary to provide a [(A1.8 fe£* Mg.7o Mn £ ) (Sk« Ali.«,)Oio(OH) 8]-0'0 positive charge sufficient to neutralize the negative tetrahedral charge may be interpreted as replacing and for analysis 129, table 2, R+2 in the 2:3 ratio, as indicated by the deficiency in the number of octahedral positions occupied. [(Al.se Ti.o* Fe & Fe & Mg,.u) Formulas like those for analyses 101 and 17, in which octahedral Al is considerably in excess of tetrahedral Al, probably represent the type of lepto- In the first formula, 0.61 Fe+3 may be interpreted chlorite that Winchell (1926) and Holzner (1938) as having replaced 0.61 Al, and 0.54 Fe+3 as having could not reduce to orthochlorite composition. For­ replaced 0.82 Mg, as indicated by the deficiency in mulas like those for analyses 148 and 128 represent total octahedral positions occupied. The second for­ the type of leptochlorite that can be partly reduced mula may be similarly interpreted; part of the Fe+3 to orthochlorite composition because of the Fe+3 (+Ti) as having replaced Al in a 1:1 ratio and present, and formulas like those for analysis 123 part as having replaced R+2 in a 2:3 ratio. represent the type that can be completely reduced From the foregoing discussion it may be con­ to orthochlorite composition, because octahedral R+3 cluded that there is great variability in the relation in excess of that needed for structural balance is due between tetrahedral and octahedral Al in chlorites. entirely to Fe+3. In relatively few chlorites is octahedral Al equiva­ Points falling below line A represent chlorites in lent to tetrahedral Al with R+2 occupying the rest which octahedral Al is lower that tetrahedral Al. of the octahedral positions, so that octahedral occu­ In such formulas other trivalent cations, like Fe+3 pancy is close to 6.00. Octahedral Al in excess of or Cr+3, are necessary to give the octahedral layers tetrahedral Al, plus any other trivalent octahedral a positive charge great enough to neutralize the cation present, such as Fe+3, replaces R+2 cations in negative tetrahedral charge. For example, in the a 2:3 ratio, and octahedral occupancy is consequently formulas for analysis 136, table 2, deficient by an equivalent amount. In other chlorites

+1.69 -1.68 octahedral Al is less than tetrahedral Al and some [(AU Fe £ Fe£. Mg.«)(Sk« Ali.6a)Oio(OH) 8] +0-<)1 other trivalent cation, usually Fe+3, is necessary for structural balance. In some of these chlorites in which octahedral Al is low, the other trivalent for analysis 45, table 2, cations are just sufficient to provide enough positive charges to balance the negative tetrahedral charge [(Al. Fe £ Fe £ Mg4.82) (Si... ALi and the octahedral occupancy is close to 6.00. In such chlorites Fe+3, or other trivalent cation, replaces Al in a 1:1 ratio. In some other chlorites in which and for analysis 70, table 2, octahedral Al is low, the other trivalent cations pres­ ent are more than sufficient to balance the negative [(Al.a Pe.lS Pe.3 tetrahedral charge and octahedral occupancy is defi­ cient. In such chlorites enough of the Fe+3 (or other all the Al and Fe+3 are necessary to provide the octa­ trivalent octahedral cation) to provide structural hedral layers with sufficient positive charge to neu­ balance replaces octahedral Al in a 1:1 ratio, and tralize the negative tetrahedral charge. In these the excess replaces R+2 in a 2:3 ratio, making the A-10 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY number of octahedral positions occupied deficient cations. For example, a chlorite having 0.20 R+3 octa­ by an amount equivalent to one-half the number of hedral cations in excess of R+s tetrahedral cations excess trivalent octahedral cations. has an octahedral occupancy of about 5.90, one with This relation between octahedral occupancy and 0.50 R+3 octahedral cations in excess has an octa­ the number of trivalent (and quadrivalent) octa­ hedral occupancy of about 5.75, and one with 1.00 hedral cations in excess of trivalent tetrahedral ca­ R+3 octahedral cations in excess has an octahedral tions is illustrated in figure 3. The points fall along occupancy of about 5.50. The points that fall farthest a straight line, showing that the deficiency in octa­ below the line represent chlorites that contain some hedral occupancy is always equal to approximately Ti, which carries two more positive charges than a one-half the number of trivalent (and quadrivalent) bivalent cation. octahedral cations in excess of tetrahedral trivalent Figure 3 also illustrates the extent to which re-

Magnesian chlorite o Intermediate chlorite x Ferroan chlorite

-0.20 5.40 5.50 5.60 5.70 5.80 5.90 6.00 6.10 OCTAHEDRAL POSITIONS OCCUPIED FIGUKB 3. Relation between octahedral occupancy and octahedral R+* (and R+i) cations in excess of tetrahedral R+8 cations. INTERPRETATION OF THE COMPOSITION AND A CLASSIFICATION OF THE CHLORITES A-ll placement of trivalent for bivalent cations in the between 3.50 and 4.00 Si positions assigned to talc- 2:3 ratio takes place in chlorites. Most chlorites show chlorites. However, in the formulas calculated from some replacement of this type; in many it is very the analyses in table 2, Si varied between 2.34 and slight, less than 0.20 octahedral positions; in others 3.45 positions, but in only one does Si occupy fewer it is moderate, between 0.20 and 0.50 positions, and than 2.40 positions (2.34), and in only one does it in a few it is even higher, with R+s cations occupying occupy more than 3.40 positions. more than 0.50 octahedral positions in excess of The relations between the number of positions those necessary for structural balance. In some chlo­ occupied by Si and the ratio Fe+2 :R+2 in the calcu­ rites these excess trivalent octahedral cations are lated formulas is shown in figure 4. Hey (1954) made up entirely of Al, in others entirely of Fe+s, divided chlorites into two series, using the arbitrary and in still others of both Al and Fe+s, assuming figure of 4 percent Fe203 as the dividing line between Al to be the primary trivalent octahedral cation, as the two types. In figure 4 the chlorites containing in the ideal formula. more than 4 percent Fe203 are distinguished sym­ RELATION BETWEEN Si AND Fe^R*2 bolically. The distribution of points in figure 4 indi­ Pauling (1930) and Brindley and Robinson (1951) cates that in chlorites in which Fe+2 :R+2 is less than state that Si occupancy of tetrahedral positions in 0.45, a Fe203 content of more than 4 percent is un­ chlorites varies between 2.00 and 3.00, but Hey usual, only 10 of 92 containing more than 4 percent (1954) classifies the chlorites within the limits of Fe2O3, but that in chlorites in which Fe2* :R+2 is more 2.00 and 4.00 Si positions per half cell, with the area than 0.45, a content of more than 4 percent Fe203

EXPLANATION

u. 20 E^a O W Fej03 < 4 percent

> 4 percent

<4 percent x > 4 Percent cr Chromian chlorite 1.00 x tx

0.80 X X

? 0.60 CE + cc. cr £ 0.40

0.20 cr x : . c.« V: 0.00 2.00 2.20 2.40 2.60 2.80 " 3.00 3.20 3.40 3.60 10 20 30 40 POSITION OCCUPIED BY Si NUMBER OF ANALYSES FIGURE 4. Relation between formula positions occupied by Si and the Fe+2 tR*2 ratio. A-12 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY is to be expected, 37 out of 55 containing more than 4 percent Fe203. The distribution of points also indi­ cates that most of the points representing chlorites in which Fe+2 :R+2 is greater than 0.50, that is, chlo­ rites in which Fe+2 is the dominant bivalent octa­ hedral cation, fall in the lower part of the Si range, below Si 2.70 (formula positions), and that most of the points representing chlorites in which Fe+2 :R+2 is less than 0.50, chlorites in which Mg is the dom­ inant bivalent octahedral cation, fall in the median part of the Si range, between Si 2.60 and 3.20 for­ mula positions, and below the Fe+2 :R+2 0.10 line. 0.00-0.10 0.11-0.30 0.31-0.50 0.51-0.70 0.71-0.90 The diagram at the top of figure 4 shows that the greatest density of points in the Si range is between

2.50 and 2.70. The 63 chlorites in which Si occupies EXPLANATION between 2.50 and 2.70 positions range in Fe2+2 : R+2 from 0.00 to 1.00 and represent a continuous and complete Mg replacement series. The greatest den­ Mg Fe+ Fe+ Al sity of points in the Fe+2 : R+2 range, as shown by the FIGURE 6. Diagrams of octahedral groups of average formulas showing diagram on the right side of figure 4, is between 0.00 transition in character from highly magnesian to highly ferroan in the and 0.10. The 56 chlorites in which Fe+2 :R+2 is 0.10 Si range 2.60-2.70. or less range in Si positions from 2.50 to 3.35 and the ratio of Fe+2 to R+2 is indicated. The diagrams represent an incomplete series in which Si and R+2 represent graphically the octahedral content of the replace R+3. Thus two principal types of replacement average formulas. Between the first formula, which are found in the chlorites, and the composition of has the composition of a very highly magnesian most chlorites can be largely interpreted in terms of chlorite, and the last formula, which has the compo­ one of these types of replacement or the other, or by sition of a very highly ferroan chlorite, there is a a combination of the two. gradual decrease in the number of positions occupied MAGNESIUM REPLACEMENT SERIES by Mg, and a gradual increase in the number of The chlorites represented by points in the most positions occupied by Fe+2. This transition in char­ populated area in the Si range, between Si 2.50 and acter, characterized by decrease in Mg and increase 2.70, vary in the ratio of Fe+2 to R+2 from 0.00 to in Fe+2, is similar to that in the trioctahedral micas 1.00, and demonstrate gradual replacement of Mg (Foster, 1960); highly magnesian chlorites being by Fe+2. The gradual transition in the chemical char­ analogous to phlogopites, intermediate chlorites be­ acter of the chlorites in this Si range is shown by ing analogous to biotites, and highly ferroan chlorites the average formulas in the following table, and by being analogous to siderophyllites and lepidomelanes. the diagrams of the octahedral groups of the aver­ Mg is replaced ion for ion by Fe+2 and, as both ions age formulas shown in figure 5. The average formu­ carry the same charge, no change in layer charge las were calculated from an average of the analyses relations, in octahedral occupancy, or in tetrahedral whose calculated formulas have Si 2.50 to 2.70, and content, is involved.

Average formulas showing transition in character from highly magnesian to highly ferroan (Si 2.50 2.70)

Average Formula (percent)

+1.87 0.00-0.10.. ii.38Fe.+d FeS i^ Al1.28)01o(OH)s] -....1.21

0.11-0.30_ a.m Mn , Al1.37)01o(OH)s] +-00 ______2.42 INTERPRETATION OF THE COMPOSITION AND A CLASSIFICATION OF THE CHLORITES A-13

Average formulas showing transition in character from highly magnesian to highly ferroan (Si 2.50 270) Continued Average Pe*2 iR*3 Formula (percent) +1.89 -1.86 0.31-0.50- _ [(Ak» Ti.oi Fe £ Fe & Mg2.« Mn.tS ) (Si2.M Al1.S8)Oio(OH) 8] +-° _.3.59

i.M Fe £ Fe & Mn .+028 ) (Si2.oo Al1.«)01o(OH) 8] +-01 -6.56

e.so

0.71-0.90___ - _ [(Ali.« Fe £ Fe fi, Mg.ra Mn £ ) (Su« AJi.»)Oio(OH)8]-ot ______7.23

fn The average formulas indicate a general increase charges. The deficiency in the total number of octa­ in Fe+3 concurrent with increase in Fe+2, from 0.09 hedral positions occupied indicates that Fe+3 can be positions in the first formula to 0.61 positions in interpreted as proxying for R+2 in a 2:3 ratio. In the last formula. However, the amount of Fe2O3 in the subsequent average formulas octahedral Al is individual chlorites throughout the Fe+2 :R+2 range slightly but increasingly deficient, and some of the varies greatly, and a given degree of replacement Fe+3 must be interpreted as proxying, 1:1, for Al. by Fe+2 has no relation to the degree of replacement In the fifth and last formula, octahedral Al is 0.23 by Fe+3. In chlorites in the 0.00 to 0.10 Fe+2 :R+2 range position less than tetrahedral Al, and approximately in which Si occupies 2.50 to 2.70 positions, Fe2O3 this much Fe+3 proxying for Al is needed for struc­ varies between 0.20 to 4.05 percent, and averages tural balance. The rest proxies for R+2 in a 2:3 1.21; in the 0.11 to 0.30 range Fe2O3 varies between ratio, as indicated by the deficiency in octahedral 0.57 to 6.84 percent and averages 2.42 percent; in occupancy. the 0.31 to 0.50 range Fe2O3 varies between 0.23 to Some individual formulas calculated from analy­ 8.59 and averages 3.59 percent, with 5 out of 16 ses that make up the averages are like the first containing more than 4 percent; in the 0.51 to 0.70 average formula in having octahedral Al equivalent range, Fe2O3 varies from none to 13.13, and averages to tetrahedral Al, and in which the Fe+3 present can 6.56 percent, with 7 out of 11 containing more than 4 be interpreted as replacing R+2 in the 2:3 ratio, with percent; in the 0.71 to 0.90 range Fe2O3 varies be­ octahedral occupancy deficient by an amount equiva­ tween 1.86 to 15.13, and averages 7.23 percent, with 9 lent to about one-half the Fe+3. Other formulas are out of 11 containing more than 4 percent. The only like the other average formulas, with some of the analyses that produced a ratio of Fe+2 to R+2 greater Fe+3 proxying for octahedral Al, ion for ion, and the than 0.90 contained 9 percent Fe2O3. Thus, although a rest replacing R+2 in the 2:3 ratio, and with octa­ chlorite in the lower part of the Fe+2 :R+2 range may hedral deficiency equivalent to one-half the Fe+3 that contain as much Fe2O3 as one in the upper part, the replaces R+2. Still other formulas have more octa­ amount of Fe2O3 usually present increases with in­ hedral Al than is necessary to neutralize the negative crease in the ratio of Fe+2 to R+2, and this is reflected tetrahedral charge. Such formulas are also charac­ in the average formulas. Even in chlorites having a terized by octahedral deficiency amounting to one- ratio of Fe+2 to R+2 less than 0.10, Fe2O3 averages half of the excess of octahedral Al over tetrahedral more than 1 percent, and 16 of the 22 chlorites Al plus any Fe+3 present, indicating that the excess having a ratio of Fe+2 to R+2 greater than 0.50 in the R+3 cations, Al or Al-j-Fe+3, have replaced R+2 ca­ Si 2.50 to 2.70 range contained more than 4 percent tions 2:3. Fe2O3. Si AND R+2 REPLACEMENT OF R*s In the average formulas there is a slight progres­ sive decrease in octahedral Al with increase in The effects that accompany change in Si content Fe+2 :R+2 ratio. In the first formula octahedral Al is are demonstrated by the chlorites represented by the exactly equal to tetrahedral Al, and thus furnishes points lying between the base line and the 0.10 the necessary number of positive charges to the octa­ Fe+2 :R+2 line in figure 4, in which Si varies from hedral layers to balance the negative tetrahedral 2.50 to about 3.40 positions. These effects are shown charge. Consequently none of the Fe+3 present, 0.09 by the average formulas in the following table, and position, is necessary to supply additional positive by the diagrams of the average formulas in figure 6. A-14 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY The average formulas are calculated from averages of the analyses whose calculated formulas have y, Fe+2 :R+2 0.10 or less, excluding those containing Cr. Theoretically increase in Si should be accompanied by an equivalent decrease in tetrahedral Al, an equiv­ alent decrease in octahedral R+3 and an equivalent increase in octahedral R+2 in accordance with the following equation: 2 Si*4 + R*3 = R+8(IV) + R+8(VI). Inspection of the average formulas shows that be­

tween the first and last there is an increase of 0.57 2.50-2.65 2.66-2.80 2.81-2.95 2.96-3.10 3.11-3.25 in Si positions, an increase of 0.49 in R+2 (domi- FORMULA POSITIONS OCCUPIED BY Si nantly Mg) positions, a decrease in 0.57 in tetra­

hedral Al positions, and a decrease of 0.52 in EXPLANATION octahedral R+s (dominantly Al) positions. These changes in composition are in good accordance with the theoretical equation. Continued increase in Si R+z R+3(VI) Si R+3(IV) and Mg and decrease in tetrahedral and octahedral FIGURE 6. Diagrams of average formulas showing change in composition of chlorites having a Pe+3 :R+a ratio of less than 0.10 with increase in Si R+3 would result in a neutral tetrahedral group com­ content. pletely occupied by Si and a neutral octahedral group These two types of ionic replacement, replacement completely occupied by Mg, Mg6.0oSi4.ooOio(OH) 8. of Mg by Fe+2 and replacement of tetrahedral and Average formulas showing change in composition with octahedral R+3 by Si and Mg, serve to interpret the increase in Si(Fe+2 :R+2 = 0.10) composition of most chlorites. In some, as in the Si Formula chlorites represented by points to the left of the Si +1.41 -1.39 2.80 line in figure 4, replacement of Mg by Fe+2 is 2.60-2.66 .[(At.*Fe.+0! Fe S Mg«.«)(Si..* Al1.39)01o(OH) 8] +0-a2 predominant. In others, as in the chlorites repre­ sented by points along the base line and below the 2.66-2.80 - Fe+2 :R+2 0.10 line, replacement of tetrahedral Al and octahedral R+3 by Si and Mg is predominant. In Fe .« Fe .»Mg«.*i Mn .«) (Si*« Al1.28)01o(OH) 8]-°-a2 still others, as in chlorites to the right of the Si 2.80 line, and above the FE+2 :R+2 0.10 line, both types of replacement are shown in some degree. Chlorites 2.81-2.95-- [ (A1.99 Fe £ Fe £ Mg,.TO) (Si2.89 AU.M) 010(OH) 8]-°-1 represented by points between Si 2.50 and 2.70 in figure 4 constitute a complete Mg replacement series, from wholly magnesian, with respect to R+2 cations, to wholly ferroan, whereas chlorites represented by 2.96-3.10 Fe S Fe S Mg4.75) (Sk« Al.87)Oio(OH) 8]-°-a2 points on or below the 0.10 Fe*2 :R+2 line consti­ tute an incomplete Si-Mg replacement series about half way between Mg4Al4Si2Oio(OH)8, amesite, and Mg6Si4Oio (OH) 8, antigorite. 3.11-3.25...... [crystal structure and are then similar in physical properties to high ferric lepto­ In the formula for analysis 135, 0.61 Fe+3 proxies chlorites. However, Hallimond (1939) believed that for octahedral Al in a ratio of 1 :1, and 0.26 for R+2 at least part of the Fe203 may be really a normal in a ratio of 2 :3, and octahedral occupancy is defici­ constituent of chlorites. More recently Hey (1954) ent by 0.13 position. In the formula for analysis 144, proposed that the arbitrary figure of 4 percent Fe203 0.02 Ti and 0.81 Fe+3 proxy for octahedral Al in a be taken as the dividing line between unoxidized and 1 :1 ratio, 0.24 Fe+3 proxy for R+2 in a 2:3 ratio, and oxidized chlorites and classified chlorites into two octahedral occupancy is deficient by 0.12 position. groups on this basis. Thus there has been some disa­ In both formulas more than two-thirds of the triva­ greement as to the status of Fe203 in chlorites, with lent iron present is essential for structural balance. a tendency to regard it an abnormal constituent. If all the Fe203 is reduced to FeO in the four Structural balance in chlorites requires that the analyses cited above, and the formulas recalculated, octahedral layers have a positive charge equivalent the formulas resulting have sufficient octahedral to the negative tetrahedral charge. To have such a charge to balance the tetrahedral charge because of positive charge, the octahedral layers must contain the excessive number of bivalent cations present, a certain minimum of trivalent cations, and if the and considerably more than 6.00 octahedral positions Al is low, the difference must be made up by other are occupied: trivalent octahedral cations, such as and usually Fe+3. In the discussion of the relation between tetra­ analysis 84, hedral and octahedral Al (p. A-7) and in figure 2 it -1.48 was shown that many chlorites do not contain as is.64 Ak«)(MOH).]- much octahedral Al as tetrahedral Al. In some of A-16 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY analysis 136, number of excess Al cations. Fe+3 cations not needed

+1.S1 -1.H. for structural balance can be accommodated in a Fe £M Mg.7i) (Sia.49 Ali.6 similar manner. Figure 3 shows that the same ac­ commodation of excess trivalent octahedral cations is found whether the excess be made up entirely of Al, analysis 135, entirely of Fe+3, or both. The relation between Fe+2 :R+2 ratio and Fe203 i Fe ifsoMg.ea Mn .£ ) (Si2.42. content in the chlorites studies is shown in figure 7. Few chlorites in which the Fe+2 :R+2 ratio is less than analysis 144, 0.45 contain more than 4 percent Fe203, only 10 out of 90, whereas two-thirds of the chlorites in which [(A1.74 Ti.os Fe ?& Mg.es) (Si2.n Fe+2 :R+2 is 0.45 or more contain more than 4 percent Fe203. It seems improbable that such a large propor­ tion of the ferrous chlorites that have been analyzed As the chlorite structure provides only 6.00 positions and studied should have undergone secondary oxi­ for octahedral cations, reduction of Fe+3 to Fe+2 dation. Many chlorites occur as secondary minerals yields irrational and unacceptable formulas for these resulting from the alteration of other species, such analyses. as olivine, pyroxene, amphibole, biotite, garnet, and Even the presence of Fe+8 cations not needed for idocrase, some of which contain Fe203, and it is to structural balance is not necessarily evidence for be expected that chlorites derived from such sources secondary oxidation. The fact that many chlorites should incorporate Fe+3 ions in their structures. The contain more octahedral Al than is required to bal­ mere presence of Fe203, or its presence in excess of ance the negative tetrahedral charge indicates that some specified amount, should not be arbitrarily the chlorite structure can accommodate an excess of attributed, therefore, to secondary oxidation. Fe+3 trivalent octahedral cations. In these chlorites, octa­ should be considered a normal constituent of chlo­ hedral Al in excess of tetrahedral Al replaces R+2 in rites, as it is considered a normal constituent of the ratio of 2 to 3, and octahedral occupancy is less other layer silicates, such as biotites, unless other than 6.00 by an amount equivalent to one-half the criteria indicate the probability of oxidation.

i.oo

X X x X EXPLANATION

X x x X Magnesian chlorite X X \ x o 0.80 x X X X 0 0 0 0 0 Intermediate chlorite o o 0 Ferroan chlorite > 0 o o o.eo 3 o o , 0^0 o o ° 0 0 c o o n n Pi f o o ° 9) c o 0 £ 0.40 3 0 0 o 0 0 o D

0.20 * * 4 *

5»*»* -14 0 , 0.00* 8 10 12 14 16 18 20 PERCENT Fe20 3

FIGURE 7. Diagram showing relation between Fe+SrB*2 ratio and FegOg in chlorites. INTERPRETATION OF THE COMPOSITION AND A CLASSIFICATION OF THE CHLORITES A-17 CLASSIFICATION OF CHLORITES between unoxidized and oxidized chlorites would SOME PREVIOUS CLASSIFICATIONS classify the formula for analysis 20, table 2, Tschermak (1890, 1891) divided the chlorites into two groups, the orthoclorites, which varied in Fe £ Fe % Mgs.TO) (Si2. composition between (Mg,Fe+2) 2Al2Si05 (OH) 4 and (Mg,Fe+2 ) 3Si2Os (OH) 4, and the leptochlorites, which as that of a thuringite, variety klementite, and the were relatively higher in trivalent cation and lower formula for analysis 22, table 2, in bivalent cation content and fell to the left of a line joining the above end members. Winchell (1926, -1.32 1936) pointed out that many leptochlorites contained .tl ) (Su.« Al considerable trivalent iron and that recomputation of the trivalent iron as bivalent iron placed them as that of a sheridanite, variety grochauite, merely among the orthochlorites. Hey (1954) divided the because one contains 0.20 percent more Fe203 (equiv­ chlorites into two series, an "unoxidized normal" alent to 0.01 formula position). Furthermore, in his series, and an "oxidized" series, with an arbitrary classification, no discrimination is made between figure of 4 percent Fe203 taken as the dividing line chlorites in which Fe+3 is required for structural between "unoxidized" and "oxidized" chlorites. Hey balance, and those in which Fe+3 is not required for subdivided the chlorites in the unoxidized series into structural balance. 11 species and 4 varieties depending on the number of Si atoms in the half-cell and the Fe : (Fe-f Mg) CLASSIFICATION BASED ON IONIC REPLACEMENTS ratio. Hey does not state the basis upon which he Many different names have been given to the chlo­ fixed the boundaries between these species and varie­ rites, principally because of differences in chemical ties. He divided the chlorites in the oxidized series composition. As it is now known that differences in into three species, based only on Si content, with chemical composition in the chlorites are attribu­ only one of these species, thuringite, being subdi­ table to ionic replacements within the same struc­ vided with respect to Fe:(Fe+Mg) ratio, thuring- tural framework, many of these names have become ites with Fe:(Fe+Mg) ratio less than 0.5 being superfluous. In a group of minerals characterized classed as a variety of thuringite, klementite. by ionic replacements special names should apply The effect of this arbitrary division of chlorites to definite, delimited, and continuous parts of the into two groups on the basis of Fe203 content is series, and not to specific points. In the trioctahedral shown in figure 8, in which the chlorites used in this micas, for example, which are characterized princi­ study are plotted according to Key's scheme, chlo­ pally by replacement of Mg by Fe+2, the term phlogo- rites containing less than 4 percent Fe203 being pite refers to the magnesian end of the series, biotite plotted in graph A, and chlorites containing more to the middle of the series, and siderophyllite or than 4 percent Fe203 being plotted in graph B. Of lepidomelane to the ferrous end of the series.1 The the chlorites used in the present study, only six with chlorites, which are characterized principally by re­ Fe:(Fe+Mg) ratios greater than 0.5 and with Si placement not only of Mg by Fe+2, but also of Al less than 2.80 have less than 4 percent Fe203. All by Si and Mg, should be classified with respect to fall in the ripidolite or ripidolite-aphrosiderite area, both replacement series. Such a scheme of classifi­ none fall in the pseudothuringite, daphnite, or cation is illustrated in figure 9, which is similar to daphnite-bavalite areas. All the other chlorites (29) figure 4, in that the co-ordinates represent the num­ with Fer(Fe-j-Mg) ratios greater than 0.50 and Si ber of positions occupied by Si and the Fe+2 :R+2 ratio, less than 2.80 have more than 4 percent Fe203 and as calculated from the number of positions occupied fall in the large, undifferentiated thuringite area. by Fe+2 and R+2 in the half-cell formula. Divisions As most ferrous chlorites contain more than 4 per­ with respect to Fe+2 :R+2 ratio are drawn at 0.25 and cent Fe2O3 and have less than 2.80 tetrahedral posi­ 0.75, making three categories, the magnesian chlo­ rites, in which Mg makes up more than 75 percent tions occupied by Si, Key's scheme leaves the great of the bivalent cations; the intermediate chlorites, majority of ferrous chlorites undifferentiated, but in which Mg makes up from 75 to 25 percent, and provides several categories for the classification of Fe+2 from 25 to 75 percent of the bivalent cations; the small minority that contain less than 4 per­ cent Fe203. 1 Annite, the ferrous analogue of phlogopite, apparently does not occur in nature because replacement of Mg by Fe+s is always accompanied by some Key's arbitrary dividing line of 4 percent Fe203 replace of Mg by Al or Fe+s. A-18 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY

S a fl -9

S* £» w

j_,K r-cO>

("IViOi) INTERPRETATION OF THE COMPOSITION AND A CLASSIFICATION OF THE CHLORITES A-19

1.00 THURINGITE x EXPLANATION ^ x CHAMOSITE X x *x X Fe2 03 <4 percent X 0.80 x. x Fe2 03 >4 percent X X cr x x % * DIABANTITE Chromia i chlorite x RIPIDOL ITE x g 0.60 3RUr&VIGITE X X x ct ( iX ^ * X x x i X X y *.* cr x "< > 0.40 X * x

0.20 X 9 * SHERIDANITE CLINOCHL ORE 4 PE^ NINITE cr X < » c? ^r- al» ;V v % 0.00 k ^ «* . f . 2.00 3.00 3.20 3.40 3.60 3.80 4.00 FORMULA POSITIONS OCCUPIED BY Si FIGURE 9. Classification of chlorites based on the two principal types of ionic replacement. and the ferroan chlorites, in which Fe+2 makes up Names applied to chlorites falling in the various areas shown more than 75 percent of the bivalent cations. These in figure 9 three categories are then subdivided with respect to Formula positions occupied by Si Si content. The analyses used in this study indicate 2.40 2.75 3.10 3.45 that chlorites seldom contain less than 2.35 Si or 1.0 Thuringite...... 9 more than 3.45 Si. Within this range of 1.10 for­ 3 2 1 mula positions between the extremes, the divisions 1 1 1 are drawn at 2.75 and 3.10, forming 3 fairly equal 1 2 divisions with respect to Si content. Thus 9 areas, 17 0.75 strictly defined with respect to Fe+2 :R+2 ratio and 12 2 Prochlorite. . . . 7 Brunsvigite. . . . 1 Si content, are provided for the classification of 4 1 Aphrosiderite . . 3 Diabantite.. .. . 1 Diabantite. . 1 chlorites. 2 1 Helminthe.. . . . 1 Pycnochlorite . . 1 The distribution of points in figure 9 shows that 11 1 6 most of the chlorites studied fall into 5 of the 9 40 areas, a sixth area is fairly well populated, but the 14 other 3 together contain only 5 points. The variety of names given to the analyzed chlo­ rites that fall in the different areas is shown in the 0.25 Sheridanite. . . . 5 Clinochlore .... 18 Penninite following chart. Of the 26 chlorites falling in the Garochauite. . . 4 Leuchtenbergi te 10 (Pennine) . . 5 Prochlorite. . . . 4 Prochlorite. . . . 2 Tabergite. . . 1 area bounded by Fe+2 :R+2 0.00-0.25 and Si 2.40-2.75, 3 2 Clinochlore .... 2 Pseudophite. . . 1 22 were designated by 8 different names, and 4 were Klementite .... 2 Sheridanite .... 1 9 1 Chlorite...... 9 called simply chlorite; of the 43 chlorites falling in 1 the area bounded by Fe+2 :R+2 0.00-0.25 and Si 2.75- 0 4 43 3.10, 34 were designated by 6 different names, and 9 26 were called chlorite; and 8 of the 14 chlorites falling in the area bounded by Fe+2 :R+2 0.26-0.75 and Si nated by a number of different names, but the same 2.76-3.10 were designated by 7 different names, with name may appear in more than one area. Corundo- the other 6 being called chlorites. Not only were the philite, ripidolite, rumpfite, leuchtenbergite, Sheri­ chlorites falling in the more populous areas desig- danite, diabantite, and clinochlore appear in 2 areas, A-20 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY chamosite and aphrosiderite in 3 areas, and thuring- 2.36-2.75 is called the thuringite area because more ite in 4 areas. Thus there seems to be considerable than one-half of the chlorites that fall in this area uncertainty among mineralogists with respect to were called thuringites. These are highly ferroan definition and delimitation of species and varieties chlorites that usually contain considerable FeaOs, in the chlorites. although a few are low in Fe203. In many of those In the classification herein proposed, species oc­ that contain considerable Fe203 some of the trivalent cupy areas delimited by Fe+2 :R+2 ratios and Si iron is necessary to structural balance. The analyses ranges, and the name chosen for a given species is given by Dana (1892) for thuringite fall in this based on usage as far as possible. For example, the area. Most of these analyses also report considerable area bounded by Fe+2 :R+2 ratio 0.00-0.25 and Si 2.76- Fe203, as much as 17.66 percent, but in one no Fe203 3.10 (see fig. 9) is called the clinochlore area, as is reported. Thus thuringite analyses in Dana like about half the chlorites falling in that area were those used in this study, range widely in Fe203 con­ called clinochlores by the authors of the papers in tent, with most of them reporting considerable Fe203, which the analyses were published. Similarly about but little MgO. In Hey's classification the name is ex­ half the chlorites falling in the area bounded by tended to include any chlorite in which Fe203 is Fe+2 :R+2 ratio 0.00-0.25 and Si>3.10 were called greater than 4 percent and Si occupies fewer than pennines or penninites, and so this area is called 2.8 positions in the half-cell formula. Thus highly the penninite area. The areas assigned to these two magnesian as well as intermediate type chlorites species correspond with the areas assigned to them become thuringites if they contain more than 4 per­ by Hey (1954) in Si ranges and in the highly mag- cent Fe203 and have less than 2.8 half-cell formula nesian character of the chlorites falling in them. positions occupied by Si. According to his classifica­ Most of the analyses listed by Dana (1892) under tion almost all the chlorites studied herein that clinochlore and penninite fall in these respective contain more than 4 percent Fe203 would be classi­ clinochlore and penninite areas. The use of no one fied as thuringites, regardless of their Fe+2 :R+2 ratios name predominates greatly over several others for because most of them have less than 2.80 Si (see chlorites falling in the area bounded by Fe+2 :R+2 fig. 9). ratio 0.00-0.25 and Si 2.36-2.75. This area approxi­ The chlorites that fall in the area bounded by mates Hey's sheridanite area, except for the some­ Fe+2 :R+2 0.26-0.75 and Si 2.76 and 3.10 were called what greater Si range, 2.36-2.75 as compared with by a variety of names (see chart p. A-19), several of Hey's 2.50-2.80, and the type sheridanite (no. 17, which, diabantite, chamosite, and ripidolite, have table 2) falls in it; consequently it is called the more appropriately been assigned to other areas. sheridanite area. As the type analysis of brunsvigite falls in this area, The area bounded by Fe+2 :R+2 ratio 0.26-0.75 and the name brunsvigite is assigned to it, and the defi­ Si 2.36-2.75 is designated the ripidolite area because nition of the name is extended to include all inter­ more of the chlorites falling in this area are identi­ mediate type chlorites (Fe+2 :R+2 0.26-0.75) with Si fied by this name than any other. As in the sheridan­ 2.76-3.10. Thus the brunsvigite area as herein de­ ite area, the Si range is somewhat greater than that fined approximates Hey's brunsvigite and pycno- for Hey's ripidolite area. Hey restricts his ripidolite chlorite areas, with no restrictions as to Fe203 area to chlorites containing less than 4 percent Fe203. content. No such restriction is made in the present classifi­ The two chlorites that fall in the area in figure 9 cation. Most of the chlorites that fall in the upper bounded by Fe+2 :R+2 0.76-1.00 and Si 2.76-3.10 were part of the area contain more than 4 percent Fe203 called thuringite and chamosite (Schmiedefeld). As (see fig. 9), so that the presence of Fe203 seems to the name thuringite has been assigned to the area be more characteristic of these chlorites than not, to the left, the name chamosite is assigned to this and in many of them some of this Fe+3 is necessary area. The name chamosite is at present under some­ for structural balance. If desired, those containing what of a cloud because some materials called chamo­ considerable Fe203 could be designated f errian ripido- site have been found to have a 7 A kaolinitelike lites. For example, in the list of locations and refer­ structure instead of the 14 A chlorite structure. ences for the analyses in table 2, ripidolites contain­ However, it is believed by the writer that as the ing more than 8 percent Fe203 are called ferrian name was originally given to what was considered ripidolites. a chlorite, and has meant a chlorite for many years, The area just above the ripidolite area in figure 9, that it should be retained as a chlorite name. which is bounded by Fe+2 :R+2 ratio 0.76-1.00 and Si The name "diabantite" is assigned to the area INTERPRETATION OF THE COMPOSITION AND A CLASSIFICATION OF THE CHLORITES A-21 bounded by Fe+2 :R+2 0.26-0.75 and Si>3.10. One of for the species that are adequately represented the chlorites that fall in this area was called diaban- among the chlorites studied are given below: tite, and the other, although given the general term "chlorite," was considered to be between diabantite Sheridanite, (Ali.e6-i.o6Fe!TO-.5o Fe^o-i-is Mg3.oo-4.7s) and delessite in composition. No name is given to the remaining area in figure 9, which contains only Clinochlore, (Ali.3B-.7oFe.oo-.so Fe*0o-.so Mg3.es-5.io) one plotted point. The chlorite represented by this point was called a thuringite, a name assigned to Penninite, (ALas-.w, Fe^oo-.os Fe^-.ss Mg3.9E-5.io) another area. Ripidolite, (Akso-.ss Fe!oo-i.iE Fei.so-s.25 Mg.7o-a.^) The presence of chromium or manganese may be noted by prefixing the species name with chromian Brunsvigite, (AU.ss-.ssFe.oo-i.io Fei.ao-s.25 Mgi.oo-2.sE) or manganian, whichever is appropriate. None of the chlorites studied contained sufficient chromium Thuringite, (Ali.s5-.s5 Fe.oo-i.so Felss-i.ao Mg.oo-.ro) or managanese to justify a special name. 'It is obvious that the composition of members of Ideally, the range for octahedral R+3 should be the a group like this cannot be adequately expressed by same as for tetrahedral R+3 and octahedral R+3 should the usual kind of mineral formulas. Such formulas be made up wholly of Al. However, the ranges for suggest minerals of definite composition, not mem­ the octahedral Al are considerably broader than the bers of a system that vary, within limits, in compo­ ranges for tetrahedral Al because of some replace­ sition, and merge into one another. The generalized ment of R+2 by Al, which results in a higher octa­ formulas shown below for members of the chlorite hedral Al than tetrahedral Al, and some replacement group show the limits of composition on the basis of of octahedral Al by Fe+3, which results in a lower the principal types of ions found in the chlorites that octahedral Al than tetrahedral Al. The distribution fa]l in the areas assigned to the respective species. of points in figure 2 shows that about one-third of For some of these generalized formulas the ranges the chlorites studied have approximately equivalent are based on a large number of formulas, for others, octahedral and tetrahedral Al, within 0.10 formula chamosite, diabantite, on only one or two. The ranges positions, but that in the other two-thirds octahedral in the number of formula positions occupied by the Al is either greater than tetrahedral Al by more than principal trivalent and bivalent octahedral cations 0.10 formula positions (points above line B) or less

Sheridanite, (R^o-i.25 R?«>-*.« ) (Si,.IM.w Alt.«^«)0»(OH)8, with Fe+2 :R+2 < 0.25;

Clinochlore, (Ri.«..so RlL-E.io ) (Si2.7^.io AW.90)Oio(OH) 8, with Fe^ :R+2 < 0.25;

Penninite, (R^-o.ss R*V..« ) (Si8.iw.« Al.8^.65)Oio(OH) 8, with Fe+2 :R+2 < 0.25,

Ripidolite, (R?«-i.« RS^.TE ) (Si...-..,. Al^^O^OIL)*, with Fe+2 :R+2 0.26-0.75,

8.00-5.80

Brunsvigite, (R^«..» Ral-s.io) (Sii.«^.io Ali.24-.9o)Oio(OH) 8, with Fe*2 :R+2 0.25-0.75,

Diabantite, (R^o-.« R£o-B.«)(Si«.:ii-«.« Al.»-.«)0,o(OH)8, with Fe+2 :H+a 0.26-0.75

Thuringite, (R^-i.as R£«.W )(Si,.«M.»Ali.«^«)0«(OH)8, with Fe+a :R+2 0.76-1.00,

Chamosite, (R^..^ Rll-E.io) (Si,.»*M Ali.M-.8o)01o(OH)s, with Fe+2 :R+2 0.76-1.00, A-22 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY than tetrahedral Al by more than 0.10 formula posi­ (Fe+2 :R+2 0.51-0.75) contain more than 4 percent tions (points below line C). In most chlorites there Fe203, and all but two of the rest contain between is less octahedral Al than tetrahedral Al. Even in 1.00 and 4.00 percent. About half of these chlorites the range formulas for chlorites that are generally are dificient in octahedral Al, and some or all of low in Fe203, like the sheridanites and clinochlores, the Fe+3 present must proxy for it, with any excess the lows for octahedral Al are 0.20 formula positions Fe+3 present proxying for R+2. In three of these lower than those for tetrahedral Al. The low for ferrous iron dominant intermediate chlorites, octa­ octahedral Al in the penninite range formula is the hedral Al is greatly in excess of tetrahedral Al, with same as that for tetrahedral Al, but in some indi­ that in excess of tetrahedral Al proxying for R+2 vidual formulas of penninites octahedral Al is less in a 2:3 ratio. Three-fourths of the ferrous chlorites than tetrahedral Al. In the range formulas for (Fe+2 :R+2 0.76-1.00) have more than 4 percent Fe203 ripidolite and thuringite, the lows for octahedral Al and only 1 of 20 has less than 1.00 percent. About are 0.40 and 0.60 positions, respectively, less than 65 percent of the ferrous chlorites are deficient in the lows for tetrahedral Al. In these species replace­ octahedral Al; several are so greatly deficient that ment of Al by Fe+3 is quite general, and may be the Al present is sufficient to supply only about half equivalent to more than one-half of the trivalent the positive octahedral charge necessary, with Fe+3 octahedral ions necessary to balance the structure. supplying the remainder. Among the whole group of Because of this proxying of Fe+3 for Al in many chlorites studied, 60 percent were deficient in octa­ chlorites, particularly in ferroan chlorites, no differ­ hedral Al, 20 percent had octahedral Al equivalent entiation is made in this scheme of classification to tetrahedral Al, and about 20 percent had octa­ with respect to Fe203 content. However, chlorites hedral Al in excess of tetrahedral Al. With respect containing considerable Fe203 could be designated to distribution as to Fe+2 :R+2 ratio, half of the chlo­ as ferrian ripidolites, thuringites, or whatever, if rites studied had a Fe+2 :R+2 ratio of less than 0.25, desired. that is, were magnesian chlorites, one-third were The relations between the Fe+2 :R+2 ratio and Fe203 intermediate chlorites, Fe+2 :R+2 0.26-0.75, with sig­ content in chlorites is shown in the following table. nificant amounts of both Mg and Fe+2, and about 13 percent were ferroan chlorites, with high Fe+2 :R+2 Relation between Fe+2 :R+2 ratio and content in chlorites ratio, above 0.75. ALLOCATION OF OCTAHEDRAL CATIONS Number of analyses having FezOs: Range of Average Fe+*:R+ s Fe20s Throughout this study the octahedral cations have ratio <1.00 1.00-4.00 >4.00 Total (percent) been grouped together in writing the formulas, as

0.00-0.25...... 29 44 5 78 1.88 have been the tetrahedral cations; no differentiation 0.26-0.50...... 2 16 13 31 4.20 has been made as to the location of the octahedral ca­ 0.51-0.75...... 2 7 16 25 6.01 tions in the octahedral layer of the mica unit and in 0.76-1.00...... 1 4 15 20 6.60 the brucite unit. Nor is such differentiation of octa­ hedral cations customarily made in writing struc­ tural formulas for chlorites, yet the way in which About one-third of the magnesian chlorites, sherdan- these cations are distributed between the two octa­ ites, clinochlores, and penninites, with Fe+2 :R+2 less hedral layers determines the amount of negative than 0.25, contain less than 1.00 percent Fe203, more and positive charges on the mica unit and on the than one-half contain between 1.00 and 4.00 per­ brucite layer respectively, and, consequently, the cent Fe203, and five contain more than 4.00 percent bonding force between the structural units. Fe203. In more than one-half of the magnesian chlo­ Pauling (1930, p. 579), in his elucidation of the rites included in this study, some or all of the chlorite structure, states that the substitution of Fe+3 present proxied for octahedral Al. Only two Al+3 for Si+4 gives the mica layers a resultant nega­ of the magnesium-dominant intermediate chlorites tive charge, as in the micas and brittle micas them­ (Fe+2 :R+2 0.26-0.50) had less than 1.00 percent Fe203, almost half had more than 4.00 percent, and the rest selves. This is compensated by the alternating bru­ had between 1.00 and 4.00 percent Fe2O3. In about cite layers, each of which through the substitution 60 percent of these chlorites, octahedral Al was defi­ of Al+3 for Mg+2 has a resultant positive charge and cient and required some other trivalent octahedral which play the same role as K+ and Ca++ in the micas ion for structural balance. About 65 percent of and brittle micas. Brindley and Robinson (1951, the ferrous iron dominant intermediate chlorites p. 180) use almost the same words with respect to INTERPRETATION OF THE COMPOSITION AND A CLASSIFICATION OF THE CHLORITES A-23 the layer-charge relations. These statements could be interpreted to mean that the negative charge on micalike unit: [(R.I KTO(Sii.« Ali.M)0M (OH),]-1- the: micalike unit is due entirely to substitution of Al43 for Si in the tetrahedral layers, that the octa­ brucitelike layer: RJfw ) 3.oi(OH) 6] +1-3 hedral layer in the micalike unit is neutral, and that all the positive charge is on the brucitelike unit, as In the formula used in these illustrations of octa­ in the following illustrations : hedral R+3 in excess of that necessary to balance the charge, the octahedral trivalent cations are made up micalike unit: [R3+2oo (Si2.B7 AkisJC of 1.64 Al and 0.14 Fe+3. As the Fe203 content is fairly low, 1.93 percent, this formula represents a brucitelike layer: [(Ri?« RJ257 )3.oo(OH) 6] +1-4S leptochlorite that cannot be completely reduced to orthochlorite composition by considering that the micalike unit: [Rs+2oo (Si3.io Al.80)Oio(OH) 2]-0-80 trivalent iron was originally bivalent. If it is postulated that the chlorite may have been brucitelike layer: [(R:Jb R2+210 KooCOH),]"-90 formed from a mica by replacing the interlayer cations with a brucitelike layer, then the micalike In such an allocation of octahedral cations, the re­ layer should have a charge of about 1.00, and the spective negative and positive charges are equivalent octahedral layer in the micalike layer should have to Al+3 replacement of Si, and, consequently, the a positive or negative charge, or be neutral, depend­ amount of charge binding the units together dimin­ ing on Al replacement in the tetrahedral layers: ishes with increase in Si content from left to right in figure 9. Thus sheridanites would be characterized +.43 -1.43 by higher layer charges than clinochlores, and clino- micalike unit: [(R$ RJfw )3.oo(Si2.BT Ali.*8)0M (OH)8]-1-co chlores by higher charges than penninites. brucitelike layer: R2+2oa )3.oi(OH) 6] +1-° In the formulas cited above, the octahedral triva- lent ions are equivalent to the tetrahedral trivalent ions and both octahedral layers are fully occupied. micalike unit: [R&, (Si..M A1.M)0U (OH),] In a great many chlorites, however, the octahedral trivalent cations exceed the tetrahedral trivalent brucitelike layer: [(R.+^ Rft. ) 3.oi(OH) 6] +9 cations, and octahedral occupancy is deficient. In the -.65 case under consideration, in which all the positive micalike unit: (Si*.« Al.B5)Oi0 (OH) 2] charge is on the brucitelike layer, the octahedral cations might be distributed as follows : brucitelike layer: R£ RJ?« )«.oo(OH).] +- If tetrahedral Al is greater than 1.00, the octahedral micalike unit: (Sis.®, Al1.32)Oio(OH)2]-1- layer in the micalike unit has a positive charge, and the composition of the unit and its layer charge rela­ brucitelike layer: 8 R& )2.79(OH) 6] +1-S6 tions resemble that of a trioctahedral mica in which there has been some trivalent octahedral substitution In this distribution of octahedral cations, the octa­ (Foster, 1960) . If tetrahedral Al is close to 1.00, the hedral layer in the micalike unit is complete, and octahedral layer in the micalike unit is neutral, or all the deficiency is in the brucitelike layer. Con­ almost so, and the composition of the unit is similar versely it is possible to so allocate the octahedral to that of phlogopite. If tetrahedral Al is consider­ cations that the deficiency is distributed between ably less than 1.00, the octahedral layer in the mica- the; two octahedral layers : like unit must also have a negative charge if the total negative charge on the unit is to approach 1.00. micalike unit: £w )2.89 (Si2.68 A11.32)010 (OH) 2]-1-3 The total negative charge is then the sum of two negative charges, one on the octahedral, one on the brucitelike layer: [(Ri?M R& ) 2.9o(OH) 6] +1-86 tetrahedral layers, as in dioctahedral micas in which there has been some bivalent ion substitution. How­ The octahedral cations may also be so allocated as ever, the composition of the micalike unit does not to throw all the deficiency on the octahedral layer in resemble that of a dioctahedral mica, because it is the; micalike unit, with the brucitelike unit com­ composed of bivalent ions, and the number of octa­ pletely occupied: hedral ions is considerably in excess of 2.00, nor does A-24 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY the composition resemble that of a trioctahedral mica consider that " * * * this is to be expected, since unit, as the octahedral layers of such micas contain the charge on the micalike layers will become smaller some trivalent ions when octahedral occupancy is with decrease in Al and the layers will not be as deficient, as in the example. tightly bonded together." It is conceivable also that neutralization of the If the octahedral layers are also identical in com­ tetrahedral charge occurs within the micalike unit, position, and successive tetrahedral and octahedral so that this unit and also the brucite layer are layers have alternating negative and positive charges neutral, as pointed out by Brindley and Gillery of the same magnitude, conversion from the 14 A (1956, p. 172) : chlorite to the 7 A kaolin type structure, or vice versa, would not require rearrangement of octa­ hedral cations, but requires only that Si atoms be micalike unit: £a ),.«,(Si..« moved from the centers of tetrahedral oxygen groups brucitelike layer: [RJ*. (OH)e]"0 to corresponding positions on the opposite side of the oxygen sheet and then linked to oxygen atoms in the adjacent brucite layer. Such a mechanism is micalike unit: R& )2.7s(Si2.e8 suggested by Brindley and Gillery (1954) to account for the series of basal X-ray reflections given by a brucitelike layer: [RJ2M (OH)e]-°° mineral called daphnite but interpreted by them as a mixed layer kaolin-chlorite structure. Such a condition seems unlikely, however, as there SUMMARY AND CONCLUSIONS is no bonding force between the constituent units. In the schemes for the distribution of octahedral Relatively few chlorites have octahedral Al ap­ cations that have been considered, the two octa­ proximately equivalent to tetrahedral Al, as is ideally hedral layers are dissimilar in composition. The only assumed; most chlorites have either more or less scheme for the distribution of octahedral cations octahedral than tetrahedral Al. In chlorites in which that produces symmetrical octahedral layers is that octahedral Al is low, some other trivalent cation, in which each species of cation is divided as equally usually Fe+3, occasionally Cr*3, must be present to as possible between the two octahedral layers : proxy for Al in providing sufficient octahedral posi­ tive charges to balance the negative tetrahedral charge. If the sum of the octahedral trivalent ca­ micalike unit: £, ),.w(Si..a A11.B8)010(OH)2]-8 tions, whether made up entirely of Al, or of Al, Fe+3, and (or) Cr+3, is about equivalent to tetrahedral Al, brucitelike layer: RJ?M )2.98 (OH) 6] +-79 octahedral occupancy is 6.00, or close to 6.00, but if the sum of the octahedral trivalent cations is greater than tetrahedral Al, octahedral occupancy is less micalike unit: [(R:B39 R& )».oo(Sii.«i Al1.i9)010 (OH)2]-6 than 6.00 by an amount about equal to one-half the brucitelike layer: [(R:B39 R*fl )3.oo(OH) 8] +-B9 excess of octahedral trivalent cations over tetrahe­ dral Al. This relationship indicates that the excess octahedral trivalent cations have replaced R+2 cations micalike unit: )>.«(Sia.> A1.77)01o(OH)2]-* in the ratio of 2:3. No correlation was found between the amount of brucitelike layer: Fe2O3 present and O content as calculated on the basis of determined H2O(-f). Some chlorites con­ In this method of allocating octahedral cations, half taining considerable Fe203 had a normal or somewhat the negative charge on the tetrahedral layers is deficient 0 content and others had less O than would neutralized within the micalike unit itself, and half be expected if the Fe2O3 were due to secondary oxi­ is neutralized by the positive charge on the brucite­ dation of FeO. In many chlorites some or all of the like layer. Thus the charge bonding force between Fe2O3 is a necessary constituent for structural bal­ the structural units is only one-half as great as in ance because of low octahedral Al. This is particu­ the first scheme considered, but, as in that scheme, larly true of ferrous chlorites, many of which contain decreases with increase in Si content. Gruner (1944) considerable Fe203. As many chlorites are formed and Bannister and Whittard (1945) correlated in­ as the result of alteration of other minerals, some of crease in the basal spacing, d (001), with increase which contain Fe2O3, it is to be expected that Fe+3 in the Si/Al(IV). Bannister and Whittard (p. 108) ions would be incorporated into the chlorite struc- INTERPRETATION OF THE COMPOSITION AND A CLASSIFICATION OF THE CHLORITES A-25 ture. Fe203 should, therefore, not arbitrarily be that has been experimentally produced. However, considered the result of secondary oxidation, but the way the octahedral cations are distributed be­ should be considered a normal constituent unless tween the two layers may differ in different types there is other evidence of secondary oxidation. of chlorites. Two series of ionic replacement characterize the REFERENCES CITED chlorites, replacement of tetrahedral and octahedral Al by Si and Mg, and replacement of Mg by Fe+2. Bannister, F. A., and Whittard, W. F., 1945, A magnesian Replacement of tetrahedral and octahedral Al takes chamosite from the Wenlock Limestone of Wickwar, place in accordance with the equation, Gloucestershire: Mineralog. Mag., v. 27, p. 99-111. Brindley, G. W., and Robinson, K., 1951, The chlorite minerals, Si + Mg = Al(IV) + Al(VI), in Brindley, G. W., ed., X-ray identification and crystal and, consequently, involves both the tetrahedral and structures of clay minerals: The Mineralog. Soc. (Clay octahedral layers and changes the layer charges; minerals group), London, p. 173-198. replacement of Mg by Fe+2 is ion for ion and in­ Brindley, G. W., and Gillery, F. H., 1954, A mixed-layer kaolin-chlorite structure, in Swineford and Plummer, volves only the octahedral layers, and causes no eds., Clays and Clay Minerals: Natl. Acad. Sci.-Natl. Re­ change in layer charges. Replacement of tetrahedral search Council Pub. 327, p. 349-353. and octahedral Al amounts to about one formula 1956, X-ray identification of chlorite species: Am. position in the group of chlorites studied, from Mineralogist, v. 41, p. 169-186. about (Alj.eoMg4.4o)(Si2.4oAli.6o)Oio(OH)8 to about Dana, E. S., 1892, The system of mineralogy, 6th ed.: New (Alo.6oMg5.4o) (Si3.4oAlo.6o)Oio(OH) 8, and is repre­ York, John Wiley and Sons, p. 649, 652, 657. sented most fully by the highly magnesian chlorites. Dschang, G. L., 1931, Die Beziehungen zwischen chemischer The replacement of Mg by Fe+2 is demonstrated most Zusammensetzung und den physikalisch-optischen Eigen- continuously and completely by chlorites in the lower schaften in der Chloritgruppe: Chemie der Erde, v. 6, part of the Si range, Si 2.50-2.75, where the full p. 416-439. range of replacement from wholly magnesian to Faust, George T., 1955, Thermal analyses and X-ray studies wholly ferroan is represented in the group studied. of griffithite: Washington Acad. Sci. Jour., v. 45, p. 66-69. Foster, M. D., 1960, Interpretation of the composition of A classification of the chlorites is based on these trioctahedral micas: U.S. Geol. Survey Prof. Paper 354-B, two series of ionic replacements. With respect to Si p. 11-49. content the chlorites are divided into three groups, Gruner, J. W., 1944, The kaolinite structure of amesite, those in which Si occupies, respectively, fewer than (OH) 8 (Mg,Fe) 4Al2 (Si2Al2)Oio, and additional data on 2.75 formula positions, between 2.75 and 3.10 for­ chlorites: Am. Mineralogist, v. 29, p. 422-430. mula positions, and more than 3.10 formula positions. Hallimond, A. F., 1939, On the relation of chamosite and With respect to Mg:Fe+2 ratio there is also a three- daphnite to the chlorite group, with chemical analyses: Mineralog. Mag., v. 25, p. 441-464. way division, the highly magnesian, with Fe+2 :R+2 Hendricks, S. B., 1939, Random structures of layer minerals less than 0.25; the intermediate, with Fe+2 :R+2 be­ as illustrated by cronstedtite (2FeO.Fe203.Si02.2H20). tween 0.25 and 0.75; and the highly ferroan, with Possible iron content of kaolin: Am. Mineralogist, v. 24, Fe+2 :R+2 greater than 0.75. This division with respect p. 529-539. to Fe+2 :R+2 ratio is similar to that of the triocta- Hey, M. H., 1954, A new review of the chlorites: Mineralog. hedral micas into phlogopites, biotites, and sidero- Mag., v. 30, p. 277-292. phyllites-lepidomelanes. The nine species into which Holzner, Julius, 1938, Beitrage zur Kenntnis der varistischen the chlorites are divided are, therefore, strictly de­ Gesteins- und Mineralprovinz im Lahn-Dillgebeit. 7. Eisenchlorite aus dem Lahngebiet; chemische Formel und fined with respect to Si content and Fe+2 :R+2 ratio. Valenzausgleich bei den Eisenchloriten: Neues Jahrb. After considerations of various schemes for the Mineralogie, Geologic u. Palaontologie, Beilage-Band 73, distribution of octahedral cations between the octa­ Abt. A., p. 389-418. hedral layer in the micalike unit and the brucitelike Mauguin, Ch., 1928, Etude des chlorites au moyen des rayons layer the equal distribution of the various kinds of X: Acad. Sci. (Paris) Comptes Rendus, v. 186,1852-1855. octahedral cations between the two octahedral layers 1930, La maille cristalline des chlorites: Soc. francaise Mineralogie Bull., v. 53, p. 279-300. seems to correlate best with the increase of basal Orcel, J., 1926, Essai de classification des chlorites: Acad. Sci. spacing, d (001), with increase in Si content that (Paris) Comptes Rendus, v. 183, p. 363-365. has been observed, and with the conversion of chlo- Pauling, Linus, 1930, The structure of the chlorites: [U.S.] rite units to two kaolin-type units and vice versa Natl. Acad. Sci. Proc., v. 16, p. 578-582. A-26 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY

Polovinkina, Y. I., and Ivanova, V. P., 1953, Chlorates and Sitzungsber., Math.-naturw. KL, Abt. I, v. 100, p. 29-107. hydromicas from Krivoy Rog.: Voprosy Petrog. i Mineral., Winchell, A. N., 1926, Chlorite as a polycomponent system: Akad Nauk SSSR, v. 2, p. 161-181 [In Russian] Am. Jour. Sci., 5th ser., v. 11, p. 283-300. Tschermak, G., 1890, Die Chloritgruppe, Teil I: Akad. Wiss. 1928, Additional notes on chlorite: Am. Mineralogist, Wien Sitzungsber., Math-naturw. Kl., Abt. I, v. 99, p. v. 13, p. 161-170. 174-267. 1936, Third study of chlorite: Am. Mineralogist, v. 21, 1891, Die Chloritgruppe, Teil II: Akad. Wiss. Wien p. 642-651. INTERPRETATION OF THE COMPOSITION AND A CLASSIFICATION OF THE CHLORITES A-27

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Percent Octahedral positions occupied by Octahedral Tetrahedral Analysis H- 1 Total Charge Al = 2, SiOa AlaOs TiOa FeaOs FeO MgO MnO CaO H20(-) HaO(+) Total Al Ti 1." F,.. Mg Mn positions Si Charge (-) (-3 W Fe+2 :R+a = 0.76-1.00 m2 135...... 20.51 19.92 10.15 34.45 3.58 0.84 0.14 10.27 99.86 1.02 0.87 3.29 0.61 0.08 5.87 1.63 2.34 1.66 hrt 136...... 20.82 17.64 Trace. . . 8.70 37.96 4.15 .07 10.31 99.65 .83 0.00 .76 3.69 .72 6.00 1.59 2.42 1.58 ^ 137...... 21.17 20.02 0.07 9.88 33.48 3.10 .45 0.10 .57 10.63 "99.65 1.14 .00 .85 3.21 .53 .04 5.77 1.54 2.43 1.57 £! 138...... 22.28 21.34 11.36 31.70 3.66 .20 Trace... 10 15 100.69 1.22 .94 2.91 .60 .02 5.69 1.54 2.45 139...... 21.71 21.35 .08 .82 43.01 2.33 .05 .16 .11 10.10 "100.07 1.40 .07 4.14 .40 .00 6.01 1.49 2.50 L50 ^ 140...... 21.66 18.56 .19 9.05 36.94 2.16 .08 Trace. . . .92 10.62 100.18 1.04 .02 .80 3.58 .37 .00 5.81 1.50 2.51 1.49 o 141...... 22.18 20.04 .04 7.35 35.23 3.79 .02 .40 .13 9.11 «99.84 1.21 .00 .63 3.35 .64 .00 5.83 1.50 2.52 1.48 \-* 142...... 22.15 22.05 .09 4.44 39.43 1.19 .22 .14 .44 9.78 « 100. 18 1.47 .00 .38 3.74 .20 .02 5.81 1.47 2.52 1.48 ^ 143...... 22.30 16.81 15.13 32.78 1.30 11 04 99.36 .88 1.32 3.18 .22 5.60 1.37 2.58 1.42 0 144...... 22.43 14.27 .19 11.98 37.63 3.42 .02 9. 70 s» 99. 90 .56 .02 1.05 3.66 .59 .00 5.88 1.41 2.61 1.39 M 145...... 23.38 19.32 2.51 38.38 .58 Trace... .48 10.62 100.66 1.20 .21 3.61 .90 .06 5.98 1.37 2.63 1.37 ^ 146...... 21.90 15.68 9.00 41.72 11 13 99.43 .85 .81 4.19 .00 5.85 1.36 2.63 1-37 H 147...... 23.43 18.21 4.49 36.30 5.41 Trace... None. . . Trace. . . 12.15 99.99 1.13 .39 3.47 .92 .00 5.91 1.34 2.68 1.32 3 148...... 24.55 22.04 Trace. . . 7.42 31.28 3.57 .04 .21 .80 9.98 99.89 1.53 .00 .61 2.86 .58 .00 5.58 1.30 2.69 1.31 2 149...... 23.32 17.45 .03 4.09 38.90 4.54 .01 .24 .80 10.89 100.27 1.06 .00 .36 3.75 .78 .00 5.95 1.32 2.69 1.31 H 150...... 24.35 20.21 .04 2.13 36.27 5.57 .48 .10 .35 10.46 99.96 1.36 .00 .18 3.38 .92 .05 5.89 1.32 2.71 1.29 o 151...... 24.72 19.94 .40 6.05 31.60 4.95 .84 .46 10 72 99.68 1.33 .03 .50 2.92 .82 .08 5.68 1.25 2.73 1.27 g 152...... 26.56 20.19 .24 1.27 36.51 2.68 2.04 .24 .40 9.97 "100.10 1.56 .02 .11 3.37 .44 .19 5.69 1.09 2.93 1.07 2 153...... 26.65 16.14 Trace... 6.69 34.43 4.47 .08 11.42 99.88 1.12 .00 .56 3.23 .75 5.66 1.00 2.99 1.01 § 154...... 30.50 18.00 .19 2.36 34.81 2.73 1.25 None. . . 10 29 52 100. 23 1.57 .02 .19 3.13 .44 .11 5.46 .72 3.28 .72 D O

1 Includes 3.90 CraOs (0.29 octahedral position) and 0.07 NiO. 25 Includes 0.54 CraOs (0.04 octahedral position) 0.09 NiO, and a trace of 2 Includes 0.14 NaaO and 0.35 KaO. NaaO. 3 Includes 0.43 NasO and 0.27 KaO. 26 A trace of PsQs. 4 Includes 0.29 NaaO and 0.23 KaO. 27 Includes 0.30 NaaO, 0.09 KsO, and 0.01 PaOs. 5 Analysis adjusted for 0.2 CaCOs. 28 Includes 0.30 PaOs. 6 Includes 0.04 KaO. 29 A trace of F present. 7 Includes 0.17 NaaO, 0.06 KaO, and 0.06 VaOs. 30 Includes 0.1 NaaO and 0.1 KaO. O 8 Includes 0.24 NaaO and O.39 KaO. 31 Includes 0.12 KaO. » Includes 1.88 CraOs (0.15 octahedral position). 32 Adjusted for 0.9 CaCOs. > 1° Includes 0.98 CraOs (0.07 octahedral position, 0.24 NiO (0.02 octahedral 33 Includes 0.11 NaaO and 0.08 KaO. position), 0.07 COa, and 0.02 F. 34 Contains 0.37 NaaO and a trace of KaO. o 11 Includes 0.03 NaaO and 0.38 KaO. 35 Contains 0.35 (NaaO + KaO). 12 Contains trace CraOs. 36 Contains 0.13 NiO (0.01 octahedral position) and traces of NaaO and 13 Includes 3.27 CraOs (0.25 octahedral position), 0.09 NiO, 0.001 LiaO, KaO. CQ 0.001 NaaO. 0.003 VaOs, and 0.001 SrO. 37 Analysis adjusted after deducting impurities. CQ 1* Includes 14.14 loss on heating, and 0.79 COa. 38 Includes 0.17 NazO and 0.17 KzO, analysis adjusted after deducting im­ 15 Includes 0.02 CraOs. purities. 16 Includes 0.14 NaaO, 1.14 CraOs (0.09 octahedral position), 0.09 NiO, 39 Ca probably from calcite in center of cavities; trace NaaO and KaO O and a trace of KaO. also present. > 17 Includes 4.16 CraOs (0.31 octahedral position). 40 Includes 0.10 KaO. H 18 Includes 0.85 CraOs (0.06 octahedral position). 41 Includes 0.61 CraOs (0.05 octahedral position). H-1 i» Includes 0.04 NaaO, 0.02 KaO, 1.10 CraOs (0.08 octahedral position) and 42 Includes 0.05 K2O. O 0.28 NiO (0.02 octahedral position). 43 Includes 0.08 NaeO and 0.12 KaO. 20 Includes 0.32 NiO (0.03 octahedral position). 44 Ca probably due to CaCOs. 45 Includes 0.12 NaaO and 0.06 K2O. 21 Includes 0.02 NaaO and 0.37 KaO. 46 Includes 0.06 NaaO and 0.12 KaO. 22 Includes 0.52 NasO, 0.15 KaO, 0.10 CraOs (0.01 octahedral position), 47 Includes 0.35 (NaaO + KaO). and 0.05 NiO. 48 Includes 0.07 NaaO, 0.02 KaO and 1.46COa. H 23 Includes 0.39 F, and 0.18 (NaaO + K2O). Summation corrected for 49 Includes 0.18 NaaO and 0.07 K2O. W (O =F) = 100.18. 50 Includes 0.22 NaaO and 0.04 KzO. M 24 Includes 0.53 NaaO, trace KaO, 0.12 CraOs (0.01 octahedral position), 51 Trace NaaO and KsO present. and 0.08 NiO. 52 Includes 0.10 (NaaO + KaO). O W

H M CQ A-30 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY

References and localities for analyses in table 2 23. Shirozu, H., 1958, Mineralog. Jour. Japan, v. 2, p. 211, no. 2, in skarn. Kamaishi mine, Iwate Pref., Japan. [In these references the locality name is quoted and the published species name is given. Species names according to the classification herein pro­ Chlorite. posed appear in center headings] 24. Simpson, E. S., 1936, Royal Soc. Western Australia Jour., v. 22, p. 3. Holleton, South-west Division, Sheridanite Western Australia. Corundophilite. 1. Iskyul, V., 1917, Experimental investigations in the 25. Okamoto, Y., and Shirozu, H., 1957, Fukuoka Univ. Fac. province of the chemical constitution of the silicates. Sci. Mem., ser. D., v. 5, p. 186. Muramatsu, Nagasaki The chlorites, Petrograd, [Mineralog. Abs. v. 2, p. Pref., Japan. Mn Leuchtenbergite. 215]. Chester, Mass. Corundophilite. 26. Button, C. O., and Seelye, F. T., 1945, Royal Soc. New 2. Phillips, W. R., 1954, Ph. D. Thesis, Univ. of Utah. Zealand, Trans. and Proc., v. 75, p. 163. Aorere, Nelson, Eldorado City, Colo., Clinochlore. New Zealand. Corundophilite. 3. Orcel, J., 1924, Acad. Sci. (Paris) Comptes Rendus, Clinochlore v. 178, p. 1729. Comberousse valley, Belledonne moun­ tains, Isere, France. Chlorite. 27. Hodl, A., 1941, Neues Jahrb. Mineralogie, Geologic, u. 4. Kurnakov, N. S., and Chernyckh, V. V., 1926, Mineralog. Palaontologie, Beil.-Band 77, Abt. A, p. 23. Oberdorf, Obshch. Zapiski v. 55, pt. 1, p. 187, no. 16, Belgium. bei St. Kathrein an-der-Laming, Styria, Austria. Klementite. Leuchtenbergite. 5. Orcel, J., 1923, Acad. Sci. (Paris) Comptes Rendus, 28. Orcel, J., 1927, Soc. franchise Mineralogie Bull. v. 50, v. 176, p. 1233. Carter's mine, Madison County, N. C. p. 347, no. 38, Table 8. Hauselberg, near Leoben, Prochlorite. Styria, Austria. Rumpfite. 6. Ross, C. S., 1935, U.S. Geol. Survey Prof. Paper 179, 29. Hodl, A., 1941, Neues Jahrb. Mineralogie, Geologic, u. p. 66. Burra Burra mine, Ducktown, Tenn. Chlorite. Palaontologie, Beil.-Band 77, Abt. A, p. 23. Kainta- 7. Pavlovitch, St., 1931, Soc. franchise Mineralogie Bull. leck, Styria, Austria. Leuchtenbergite (Klinochlor). 53, p. 536. Corundum Hill, Macon County, N. C. 30. Iskyul, V., 1917, Experimental investigations in the pro­ Grochauite. vince of the chemical constitution of the silicates. The 8. Lacroix, A., 1922, Acad. Sci. (Paris) Comptes Rendus, chlorites, Petrograd, [Mineralog. Abs. v. 2, p. 215]. v. 174, p. 903. Antohidrano, Madagascar. Grochauite. Nizhne-Issetsk estate, Urals, Russia. Clinochlore. 9. Shannon, E. V., and Wherry, E. T., 1922, Washington 31. Garrido, J., 1949, Soc. franchise Mineralogie et Crystal- Acad. Sci. Jour., v. 12, p. 240. Wyoming (?) Sheri­ lographie Bull. v. 72, p. 551. Sierra de la Capelada, danite. Galicia, Spain. Chlorite. 10. Phillips, W. R., 1954, Ph. D. Thesis, Univ. of Utah. 32. Phillips, W. R., 1954, Ph. D. Thesis, Univ. of Utah. Har- Miles City, Mont. Sheridanite. ford County, Md. Prochlorite. 11. Pavlovitch, St., 1931, Soc. franchise Mineralogie Bull., 33. Harada, Z., 1959, Hokkaido Univ. Fac. Sci. Jour., ser. 4, v. 53, p. 537. Kalinski, Urals, Russia. Grochauite. v. 10, p. 80. Wanibuchi mine, Hirata City, Simana 12. Shannon, E. V., and Wherry, E. T., 1922, Washington Pref., Japan. Chlorite. Acad. Sci. Jour., v. 12, p. 240. Brinton's Quarry, 34. Orcel, J., 1927, Soc. franchise Mineralogie Bull., v. 50, Chester County, Pa. White chlorite. p. 201. Ambatofinandrahana Prov., Madagascar. Pro­ 13. Hodl, A., 1941, Neues Jahrb. Mineralogie, Geologic u. chlorite. Palaontologie, Beil.-Band 77, Abt. A, p. 24. Hausel- 35. Kurnakov, N. S., and Chernykh, V. V., 1926, Mineralog. berg, near Loeben, Styria, Austria. Grochauite. Obshch. Zapiski, v. 55, pt. 1, p. 187, no. 4. Achmatovsk, 14. Orcel, J., 1927, Soc. franchise Mineralogie Bull., v. 50, Nazyamisk mountains, southern Urals, Russia. Clino­ p. 206. Carter mine, Democrat, N. C. Prochlorite. chlore. 15. Iskyul, V., 1917, Experimental investigations in the pro­ 36. Orcel, J., 1925, Acad. Sci. (Paris) Comptes Rendus, v. vince of the constitution of the silicates. The chlorites. 180, p. 1673. Midongy, Ambatofinandrahana Prov., Petrograd, [Mineralog. Abs. v. 2, p. 215]. Meerbrecht, Madagascar. Leuchtenbergite. Tyrol. Prochlorite. 37. Clarke, F. W., 1910, U.S. Geol. Survey Bull. 419, p. 293, 16. Orcel, J., 1927, Soc. franchise Mineralogie Bull., v. 50, C. Slatoust, Urals, Russia. Leuchtenbergite. p. 216. Leydsdorp district, Transvaal, [Union of South 38. Shirozu, H., 1958, Mineralogical Jour. Japan, v. 2, p. 211, no. 3. Sann5, Fukuoka Pref., Japan. Chlorite. Africa], Prochlorite. 39. Shirozu, H., 1958, Mineralogical Jour. Japan, v. 2, 17. Wolff, J. E., 1912, Am. Jour. Sci., ser. 4, v. 34, p. 476. p. 211, no. 5. Wakimisaki, Nagasaki Pref., Japan. Northern Wyoming. Sheridanite. Chlorite. 18. Phillips, W. R., 1954, Ph. D. Thesis, Univ. of Utah. 40. Iskyul, V., 1917, Experimental investigations in the pro­ Chester, Vt. Prochlorite. vince of the chemical constitution of the silicates. The 19. Orcel, J., 1927, Soc. franchise Mineralogie Bull., v. 50, chlorites, Petrograd, [Mineralog. Abs. v. 2, p. 215]. p. 347, no. 37, table 8. Hauselberg, near Leoben, Nazyamsk mountains, Urals, Russia. Clinochlore. Styria, Austria. Rumpfite. 41. Iskyul, V., 1917, Experimental investigations in the pro­ 20. Dschang, G. L., 1931, Chemie der Erde, v. 6, p. 420, vince of the chemical constitution of the silicates. The no. 2. Achmatowsk, Urals, Russia. Clinochlore. chlorites, Petrograd, [Mineralog. Abs. v. 2, p. 215]. 21. Melon, J., 1938, Acad. royale Belgique cl. sci., Mem. Shishimsky mine, southern Urals, Russia. Leuchten­ (in-8°), v. 17, p. 23. Regne, Belgium. Chlorite. bergite. 22. Melon, J., 1938, Acad. royale Belgique cl. sci. Mem. 42. Hla, T., 1945, Mineralog. Mag., v. 27, p. 139. West (in-8°), v. 17, p. 19. Vielsalm, Belgium. Klementite. Chester, Pa. Clinochlore. INTERPRETATION OF THE COMPOSITION AND A CLASSIFICATION OF THE CHLORITES A-31

43. Dschang, G. L., 1931, Chemie der Erde, v. 6, p. 420, 65. Vavrinecz, G., 1927, Magyar Chemiai Folyoirat, Buda­ no. 3. West Town, Pa. Clinochlore. pest, v. 33, p. 186, no. 1. Bernstein, Austria. Pseudo- 44. Serdyuchenko, D. P., 1953, Chlorites, their chemical con­ phite. stitution and classification, Izdel. Akad. Nauk. SSSR 66. Sato, S., 1933, Shanghai Sci. Inst. Jour., sec. 11, v. 1, Moscow, p. 176, table 60, no. 2. Angar river, U.S.S.R. p. 18. Near Syunkodo, Korea. Leuchtenbergite. Chlorite. 67. Hutton, C. 0., 1947, Royal Soc. New Zealand Trans. and 45. Kitahara, J., 1955, Japanese Assoc. Mineralogists, Pe- Proc., v. 76, p. 488, no. 1. Kaukapakapa, North Auk- trologists, and Economic Geologists Jour., v. 39, p. land, New Zealand. Leuchtenbergite. 173. Hinokami mine, Tari district, Tottori Pref., 68. Shirozu, H., 1958, Mineralog. Jour. Japan, v. 2, p. 211, Japan. Leuchtenbergite. no. 4. Okusi, Nagasaki Pref. Japan. Chlorite. 46. Orcel, J., 1927, Soc. franchise Mineralogie Bull., v. 50, 69. Simpson, E. S., 1936, Royal Soc. Western Australia p. 353, no. 73, table 13. Rauenthal, Markirch, Alsace, Jour., v. 22, p. 3. Ninghanboun Hills, Southwest Divi­ France. Clinochlore. sion, Western Australia. Clinochlore. 47. Osborne, F. F., and Archambault, M., 1948, Royal Soc. Penninite Canada Trans., ser. 3, v. 42, sec. 4, p. 66. Mount Albert, Quebec, Canada. Clinochlore. 70. Kurnakov, N. S., and Chernykh, V. V., 1926, Mineralog. 48. Durrell, C., and MacDonald, G. A., 1939, Am. Mineralo­ Obshch. Zapiski v. 55, p. 187, no. 2. Shishimsk moun­ gist v. 24, p. 454. Near Kings River, Calif. Clinochlore. tains, Zlatoust region, southern Urals, Russia. Penni­ 49. Clarke, F. W., 1910, U.S. Geol. Survey Bull. 419, p. 293, nite. B. Nikolai-Maximilian mine, Slatoust district, Urals, 71. Dschang, G. L., 1931, Chemie der Erde, v. 6, p. 420, no. 6. Russia. Clinochlore. Locality not given. Pennine. 50. Serdyuchenko, D. P., 1953, Chlorites, their chemical con­ 72. Lapham, D. M., 1958, Am. Mineralogist, v. 43, p. 923. stitution and classification, Izdel. Akad. Nauk SSSR., Zermatt, Valais, Switzerland. Chromian chlorite. Moscow, p. 176, table 60, no. 1. Angar river, U.S.S.R. 73. Ivanova, V. P., 1949, Akad. Nauk SSSR. Geol. Inst. Chlorite. Trudy, v. 120, p. 63. Location not given. Penninite. 51. Rondolino, R., 1936, Periodico Mineralog., Roma, v. 7, 74. Iskyul, V., 1917, Experimental investigations in the pro­ p. 199. Piampaludo, Piedmont, Italy. Clinochlore. vince of the chemical constitution of the silicates. The 52. Ivanova, V. P., 1949, Akad. Nauk SSSR Geol. Inst., chlorites, Petrograd, [Mineralog. Abs. v. 2, p. 215]. Trudy, v. 120, p. 63. Location not given. Leuchten­ Pfitschtal, Tyrol. Pennine. bergite. 75. Ivanova, V. P., 1949, Akad. Nauk SSSR Geol. Inst. 53. Tajder, M., 1938, Inst. Geol. Kraljevine Jugoslavije Trudy, v. 120, p. 63. Location not given. Tabergite. Vesnik, v. 6, p. 235. Dobro Polje, Serbia, Yugoslovia. 76. Lapham, D. M., 1958, Am. Mineralogist, v. 43, p. 923. Clinochlore. Chester County, Pa. Chromian chlorite. 54. Kitahara, J., 1955, Japanese Assoc. Mineralogists, Pe- 77. Bertolani, M., 1949, Comit. Sci. Centr. Club. Alpino trologists, and Economic Geologists Jour., v. 39, p. 169, Italiano Modena, Mem. no. 1, p. 53. Secchia valley, Ap- Hinokami mine, Tare district, Tottori Pref.; Japan. pennines region, Italy. Pennine. Leuchtenbergite. 78. Lapham, D. M., 1958, Am. Mineralogist, v. 43, p. 923. 55. Du Rietz, T., 1935, Geol. Foren. Stockholm Forh., v. 57, Ogushi, Hizen, Japan. Chromian chlorite. p. 188. Muruhatten, Sweden. Clinochlore. Ripidolite 56. Orcel, J., 1927, Soc. franchise Mineralogie Bull., v. 50, 79. Hodl, A., 1941, Neues Jahrb. Mineralogie, Geologie, u. p. 267. South of Maevatanana, Madagascar. Clino­ Palaontologie, Beil.-Band 77, Abt. A, p. 26. Klein- chlore. Litzner, Silvretta, Tyrol-Voralberg. Prochlorite. 57. Lapham, D. M., 1958, Am. Mineralogist, v. 43, p. 923. West Chester, Pa. Chromian chlorite. 80. Hodl, A., 1941, Neues Jahrb. Mineralogie, Geologie, u. 58. Orcel, J., Acad. Sci. (Paris) Comptes Rendus, v. 180, Palaontologie, Beil.-Band 77, Abt. A, p. 27. Granit- p. 837. Patevi, 20 km. SSE of Atakpame, Togo, Africa. zer, near Weiz, Styria, Austria. Fe-prochlorite. Clinochlore. 81. Melon, J., 1938, Acad. royale Belgique Bull. cl. sci. Mem. 59. Hutton, C. 0., 1936, Royal Soc. New Zealand Trans. and (in-8°), v. 17, no. 4, p. 25, no. 3. Serpont Recogne, Proc., v. 66, p. 36. Red Mountain, south Westland, Belgium. Chlorite. New Zealand. Chlorite. 82. Phillips, W. R., 1954, Ph. D. Thesis, Univ. of Utah. 60. Ivanova, V. P., 1949, Akad. Nauk. SSSR. Geol. Inst. Chester, Mass. Corundophilite. Trudy, v. 120, p. 63. Location not given. Clinochlore. 83. Holzner, J., 1938, Neues Jahrb. Mineralogie, Geologie, u. 61. Orcel, J., 1925, Acad. sci. (Paris) Comptes Rendus, Palaontologie, Beil.-Band 73, Abt. A, p. 401, no. 2. v. 180, p. 837. Patevi, 20 km. SSE of Atakpame, Togo, Georg-Joseph, Lahn-Dillgebiet, Germany. Aphrosid- Africa. Clinochlore. rite. 62. Smith, W. C., 1924, Mineralog. Mag. v. 20, p. 242. Bern­ 84. Vavrinecz, G., 1932, Maygar Chemiai Folyoirat, Buda­ stein, Austria. Clinochlore. pest, v. 38, p. 143, no. 5. Zillerthal, Austria. Helminthe. 63. Phillips, W. R., 1954, Ph. D. Thesis, Univ. of Utah. 85. Ontoev, D. 0., 1956, Akad. Nauk SSSR Izv. ser. geol. Brewster, N. Y. Clinochlore. no. 4, p. 46, no. 1. Shadskaya, U.S.S.R. Thuringite. 64. Serdyuchenko, D. P., 1953, Chlorites, their chemical 86. Phillips, W. R., 1954, Ph. D. Thesis, Univ. of Utah. constitution and classification, Izdel. Akad. Nauk Simplon Tunnel, Switzerland. Prochlorite. SSSR, Moscow, p. 147, table 47, no. 1. Beskes river, 87. Shirozu, H., 1958, Mineralog. Jour. Japan, v. 2, p. 212, U.S.S.R. Chlorite. no. 10. Sayama mine, Akita Pref., Japan. Chlorite. A-32 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY

88. Sudo, T., 1943, Chemical Soc. Japan Bull., v. 18, p. 289. 113. Holzner, Julius, 1938, Neues Jahrb. Mineralogie, Geolo­ Tateyama Hot Springs, Jodojama, Toyama Pref., gie, u. Palaontologie, Beil-Band 73, Abt. A, p. 401, Japan. Mn-thuringite. no. 1. Weilburg, Lahn-Dillgebiet, Germany. Aphro­ 89. Phillips, W. R., 1954, Ph. D. Thesis, Univ. of Utah. siderite. Southbury, Conn. Prochlorite. 114. Orcel, J., 1927, Soc. francaise Mineralogie Bull., v. 50, 90. Clarke, F. W., 1910, U.S. Geol. Survey Bull. 419, p. 294. p. 257. Evisa, Corsica. Thuringite. Aqueduct Tunnel, Washington, D. C. Prochlorite. 115. Larsen, E. S., and Steiger, G., 1917, Washington Acad. 91. Hodl, A., 1941, Neues Jahrb. Mineralogie, Geologie, u. Sci. Jour., v. 7, p. 10. Last Chance mine, Creede, Colo. Palaontologie, Beil.-Band 77, Abt. A, p. 25, no. 4. Thuringite. Shottgraben near Frohleiten, Styria, Austria. Pro­ 116. Serdynchenko, D. P., 1953, Chlorites, their chemical con­ chlorite. stitution and classification, Izdel. Akad. Nauk SSSR, 92. Melon, J., 1938, Acad. royale Belgique cl sci. Mem. Moscow, p. 163, table 54, No. 3. Northern Urals, (in-8°), v. 17, p. 31. Nil-Saint-Vincent, Belgium, Russia. Chlorite. Chlorite. 117. Ivanova, V. P., 1949, Akad. Nauk SSSR, Geol. Inst. 93. Lazarenko, E. K., 1950, Akad. Nauk SSSR Doklady, Trudy, v. 120, p. 65. Location not given. Ripidolite. v. 72, no. 4, p. 772, San-Donato, Urals, U.S.S.R. 118. Shirozu, H., 1958, Mineralog. Jour. Japan, v. 2, p. 212, Corundophilite. no. 8. Osaruzawa mine, Akita Pref., Japan. Ripidolite. 94. Agar, W. M., and Emendorfer, E. H., 1937, Am. Jour. Brunsvigite Sci. ser. 5, v. 34, p. 79. Hawleyville, Conn. Prochlorite. 95. Serdyuchenko, D. P., 1953, Chlorites, their chemical con­ 119. Orcel, J., 1927, Soc. franchise Mineralogie Bull., v. 50, stitution and classification, Izdel. Akad. Nauk SSSR, p. 231. La Croix, Isere, France. Ripidolite. Moscow, p. 163, Table 54, no. 4. Northern Urals, 120. Hutton, C. 0., 1938, Mineralog. Mag., v. 25, p. 198. U.S.S.R. Chlorite. Summitt of Coronet Peak, Wakatipu region, western 96. Ivanova, V. P., 1949, Akad. Nauk SSSR Geol. Inst. Otago, New Zealand. Chlorite. Trudy, v. 120, p. 69, Location not given. Ripidolite. 121. Harada, Z., 1959, Hokkaido Univ. Fac. Sci. Jour., ser. 4, 97. Ivanova, V. P., 1949, Akad. Nauk SSSR Geol. Inst. v. 10, p. 80. Syogase, Ino town, Agawa country, Koti Trudy, v. 120, p. 69. Location not given. Ripidolite. Pref., Japan. Chlorite. 98. Phillips, W. R., 1954, Ph. D. Thesis, Univ. of Utah. 122. Melon, J., 1938, Acad. royale Belgique cl. sci., Mem. Goscheneralp, Switzerland. Ripidolite. (in-8°), v. 17, no. 4, p. 28. Lembecq, Belgium. Chlorite. 99. Orcel, J., 1927, Soc. francaise Mineralogie Bull. 50, p. 123. Bannister, F. A., and Whittard, W. F., 1945, Mineralog. 360, table 17, no. 100. Kasbek, Caucasus, Russia. Mag., v. 27, p. 102, no. 2. Wickwar, Gloucestershire, Ripidolite. England. Magnesian chamosite. 100. Orcel, J., 1927, Soc. francaise Mineralogie Bull. 50, p. 124. Macgregor, A. M., 1941, Mineralog. Mag. v. 26, p. 103. 252. Weilburg, Nassau, Germany. Aphrosiderite. Old West mine, Penhalonga, Southern Rhodesia. Chlo­ rite. 101. Frankel, J. J., 1944, Chemical, metallurgical and mining Soc., South Africa Jour., v. 44, p. 173. Witwatersrand, 125. Fromme, J., 1903, Tschermaks mineralog. petrog. Mitt., South Africa. Chlorite. v. 22, p. 62. Radauthal, Harz, Germany. Pykno- chlorite. 102. Korzhynskiy, A. F., 1959, Akad. Nauk SSSR, Sibirskoye Otdel. Vostochno-Sibirskiy Geol. Inst. Zapiski, p. 51, 126. Kosik, S., 1930, Acad. Polonaise Sci., Lettres, cl. sci. no. 1. Kholtason, Dzhidy, Russia. Ripidolite. math, nat. Bull., ser. A, p. 540. Slawkowska valley, 103. Orcel, J., 1927, Soc. franchise Mineralogie Bull. 50, p. West Tatra mountains. Delessite. 357, table 14, no. 81. Laifour, Ardennes, France. 127. Serdyuchenko, D. P., 1953, Chlorites, their chemical con­ Ripidolite. stitution and classification, Izdel. Akad. Nauk SSSR, 104. Ivanova, V. P., 1949, Akad. Nauk SSSR., Geol. Inst. Moscow, p. 34, table 5. Mozikei river, Russia. Chlorite. Trudy, v. 120, p. 69. Location not given. Ripidolite. 128. Kosik, S., 1930, Acad. Polonaise Sci., Lettres, cl. sci. 105. Orcel, J., 1927, Soc. francaise Mineralogie Bull. 50, p. math, nat. Bull., ser. A, p. 538. Wolowiec, West Tatra 238, table 14, no. 82. Presqu'ile Masoala, Madagascar. Mountains. Chlorite. Ripidolite. 129. Holzner, J., 1938, Neues Jahrb. Mineralogie, Geologie, u. 106. Button, C. 0., 1938, Mineralog. Mag. v. 25, p. 198. Palaontologie, Beil.-Band 73, Abt. A, p. 405. Ernst- Kawarau survey district, Western Otago, New Zea­ hausen, Lahn-Dillgebiet, Germany. Aphrosiderite. land. Chlorite. 130. Shannon, E. V., 1920, U. S. Natl. Mus. Proc. v. 57, p. 107. Ross, C. S., 1935, U.S. Geological Survey Prof. Paper 399, Westfield, Mass. Diabantite. 179, p. 66. Ore Knob, N. C. Chlorite. 131. Ivanova, V. P., 1949, Akad. Nauk SSSR Geol. Inst. 108. Seitsaari, Juliani, 1954, Comm. Geol. Finlanda Bull., Trudy, v. 120, p. 72. Location not given. Aphrosiderite. no. 166, p. 79. Kangasala, Finland. Chlorite. 132. Fromme, J., 1902, Tschermaks mineralog. petrog. Mitt., 109. Orcel, J., 1927, Soc. francaise Mineralogie Bull., v. 50, v. 21, p. 171. Radauthal, Harz, Germany. Brunsvigite. p. 358, table 15, no. 88. Dragset, Norway. Ripidolite. 110. Orcel, J., 1927, Soc. franchise Mineralogie Bull., v. 50, Diabantite p. 228. Androta, Madascar. Ripidolite. 133. Tomkeieff, S. I., 1943, Irish Naturalists Jour. v. 8, p. 71. 111. Shirozu, H., 1958, Mineralog. Jour. Japan, v. 2, p. 212. Doon Point, Murlough Bay, Ireland. Diabantite. Besshi mine, Ehime Pref., Japan. Chlorite. 134. Ross, C. S., and Shannon, E. V., 1924, U. S. Natl. Mus. 112. Ivanova, V. P., 1949, Akad. Nauk SSSR. Geol. Inst., Proc., v. 64, p. 15. Challis, Custer County, Idaho. Trudy, v. 120, p. 69. Location not given. Ripidolite. Chlorite. INTERPRETATION OF THE COMPOSITION AND A CLASSIFICATION OF THE CHLORITES A-33

Thuringite 145. Shiroza, H., 1958, Mineralog. Jour. Japan, v. 2, p. 212, 135. Hodl, A., 1941, Neues Jahrb. Mineralogie, Geologie, u. no. 11. Kishu mine, Mie Pref., Japan. Thuringite. Palaontologie, Beil.-Band 77, Abt. A, p. 28. Goldzeche, 146. Kurnakov, N. S., and Chernykh, V. V., 1926, Mineralog, Rauriser Sonnblickgebiet, Carinthia, Austria. Thurin- Obshch. Zapiski, v. 55, Pt. 1, p. 187, no. 13. Schmiede­ gite. feld, eastern Thuringia, Germany. Thuringite. 136. Jung, H., and Kohler, E., 1930, Chemie der Erde, v. 5, 147. Simpson, E. S., 1936, Royal Soc. Western Australia Jour., p. 186. Schmiedefeld, Thuringia, Germany. Thuringite. v. 22, p. 3. Randalls, Central Division, Western Aus­ 137. Simpson, E. S., 1937, Royal Soc. Western Australia tralia. Daphnite. Jour., v. 23, p. 21. Mount Satirist, Northwest divi­ 148. Slavik, F., and Vesely, V., 1923, Narodniho Musea sion, Australia. Aphrosiderite. Casopis, v. 97, p. 136. Ouvaly, east of Prague, Czecho­ 138. Hodl, A., 1941, Neues Jahrb. Mineralogie, Geologie, u. slovakia. Aphrosiderite. Palaontologie, Beil.-Band 77, Abt. A., p. 27. Zirmsee, 149. Simpson, E. S., 1936, Royal Soc. Western Australia Rauriser Sonnblickgebiet, Carinthia. Thuringite. Jour., v. 23, p. 22. Kalgoorlie, Western Australia. 139. Orcel, J., 1923, Acad. Sci. (Paris) Comptes rendus, v. 177, p. 272. Bas Vallon, near Quintin, Brittany, Daphnite. France. Thuringite. 150. Hallimond, A. F., 1939, Mineralog. Mag. v. 25, p. 443. 140. Ivanova, V. P., 1949, Akad. Nauk SSSR. Geol. Inst. Tolgus mine, Cornwall, England. Daphnite. Trudy, v. 120, p. 72. Location not given. Thuringite. 151. Phillips, W. R,, 1954, Ph. D. Thesis, Univ. of Utah. 141. Holzner, J., 1938, Neues Jahrb. Mineralogie, Geologie, u. Dona Ana County, N. Mex. Thuringite. Palaontologie, Beil.-Band 73, Abt. A, p. 403, no. 3. Chamosite Fortuna, Lahn-Dillgebiet, Germany. Thuringite. 142. Ontoev, D. 0., 1956, Akad. Nauk SSSR Izv., ser. geol., 152. Ivanova, V. P., 1949, Akad. Nauk SSSR Geol. Inst. no. 4, p. 46, no. 2. Ostrogorskaya, U.S.S.R. Thuringite. Trudy, v. 120, p. 72. Location not given. Thuringite. 143. Zalinsky, E. R., 1904, Neues Jahrb. Mineralogie, Geolo­ 153. Jung, H., 1931, Chemie der Erde, v. 6, p. 281. Schmiede­ gie, u. Palaontologie, Beil.-Band 19, p. 71. Schmiede­ feld, Thuringia, Germany. Chamosite. feld, Thuringia, Germany. Thuringite. 144. Deverin, Louis, 1945, Mater. Geol. Suisse, Ser. Geotechn, Not named v. 2, no. 13, p. 89. Windgalle, Maderanerthal, Uri, 154. Ivanova, V. P., 1949, Akad. Nauk SSSR Geol. Inst. Switzerland. Chamosite. Trudy, v. 120, p. 72. Location not given. Thuringite.

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