MINERAL CHEMISTRY AND MINERALOGY OF THE LEAD BEARING MEMBERS OF THE BEUDANTITE AND RELATED MINERAL GROUPS.
By
W.E. BAKER
B.Sc. Hon (Tas.), M.Aus.I.M.M.
A thesis presented for the Degree of Master of Science, The University of New South Wales.
September, 1962. PLATE 1
Dundas Pyromorphite showing pseudomorphous Hinsdalite, a Beudantite Group mineral, at low centre (x2). CONTENTS
Page
Summary 1 •
Introduction 4.
Part I - Mineral Synthesis 11.
Part II - Studies of Mineral Equilibria 23*
Part III - Mineralogical Studies 49.
Part IV - Concluding Remarks 96.
Appendix - Analytical Procedures and Detailed Results 104.
References 124.
(iii) SUMMARY.
Following the recognition of a pseudomorph after pyro-
morphite from Dundas, Tasmania, as being either hinsdalite
PbAl^CPO^) (SO^) (OH)^ or plumbogummite PbAl^(P0jL+)2(0H) H^O,
a general study of these and related minerals was under
taken.
The minerals, beudantite, PbFe^(AsO^)(SO^)(OH)^, cork-
ite, PbFe^(PO^)(SO^)(OH)^, hinsdalite and hidalgoite PbAl^
(AsO^)(SO^)(OH)^, all members of the Beudantite Group, were
synthesized as were also the compounds PbAl^CVO^)(SO^)(OH)^
and PbFe^CVO^)(SO^)(OH)^. Synthesis of plumbogummite and
its iron analogue PbFe^(POi+)p(OH)^.H^O were also successful
but attempts to produce the chromium analogues of these min
erals and compounds related to plumbojarosite PbFe^CSG^)^
(0H)12 failed.
Specimens of hinsdalite, plumbojarosite and the syn thetics were examined by means of X-ray diffraction and the rhombohedral cell constants found to be:
Hinsdalite = 61°8 1 arh = 6,88 a Hidalgoite 6*97 60°43
Corkite 7.00 63°00
Beudantite 7.08 62°36
PbAl3(V04)(S04)(0H)6 7.00 60°20
PbFe3(V04)(S04)(0H)6 7-12 62°24
Plumbogummite 6.90 61 °8' 2. PbFe3(P04)2(0H)^.H20 7.04 63°36
Plumbojarosite 11.94 35°00 It was not found possible to distinguish between hinsdalite and plumbogummite on the basis of X-ray results. The pres ence of water in only the latter mineral indicated that differential thermal analysis might detect the difference and this was found to be the case.
The formation of hinsdalite, corkite and pyromorphite was subjected to physico-chemical studies which enabled the calculation of the free energies of formation of these min erals as -1034.4, -669*8 and -842.3 k.cal. respectively. These values were used to test the feasibility of a volume constant reaction proposed to explain the alteration of pyromorphite to hinsdalite. -| # 9Pb?(P04) Cl + 72A13+ + 24S0^_ + 1440H“ (+ 24C1_) ^ 24PbAl (P04)(S01+)(0H)6 + 21Pb2+ + 3P0^_ + 9CI (+24C1-).
The reaction was found to result in a decrease in free energy and would thus be a spontaneous process. Hence it is likely that the equation demonstrates the manner in which the alteration of pyromorphite took place in the oxidized zone.
The genesis of either hinsdalite or plumbogummite re quires the presence of abundant aluminium which is not a
1. Bracketed chloride ions included only to preserve elec trical neutrality. • 3- common metal in either the hydrothermal or oxidation envir onment. The abundance of the eLement in the Dundas area is indicated by the widespread occurrence of gibbsite. The origin in this case is possibly to be found in the hydro- thermal alteration of the eugeosynclinal sediments with which the Dundas ore-bodies are associated. Since hinsdal- ite and plumbogummite both appear to be formed quite readily the mineral which is produced may depend largely upon the time of entry of the aluminium into the environment. If this occurs during the oxidation of the ore-body then the abundance of sulphate will favour the formation of hinsdal- ite. Once the sulphides have been oxidised down to the water table, the concentration of sulphate in the ground water will fall to a far lower level and, provided that sufficient phos phate is present, the formation of plumbogummite will be favoured. 4. INTRODUCTION.
The data presented in this thesis have resulted from the.study of a number of the less common secondary lead min erals. The investigations began in 1957 whilst the writer was a teaching fellow at the University of New South Wales and were completed at Broken Hill in 1961. The programme was initiated by the study of a specimen from the Comet 0 Mine, Dundas, Tasmania *. This consisted largely of a pale green mass of hexagonal prisms of pyromorphite distributed through a limonitic gossan. In parts of the specimen there were white pseudomorphs after pyromorphite, some of them occurring merely as thin shells of hexagonal outline.
(Plate 1, frontispiece.) A qualitative spectrographic examination of the pseudo- morph showed that the dominant metals were aluminium and lead whilst silver was present as a minor constituent. X-ray powder diffraction data were obtained by means of a Phillips
Model 1050 X-Ray Diffractometer. Comparison of these data with those available in the A.S.T.M. Card Index showed that plumbogummite, PbAl^(PO^)^(OH) H^O (Card 2-O683), gives a similar diffraction pattern and has a composition compatible with the spectrographic results for the pseudomorph.
2. Examination of the specimen was requested by Associate Professor L.J. Lawrence, then Senior Lecturer in charge of the Geological Section of the School of Mining Eng ineering and Applied Geology. .?• Plumbogummite is a member of one of three isostruct-
ural groups of minerals, namely the Alunite, Plumbogummite
and Beudantite Groups. As is the case with the Plumbo
gummite Group the other two take their names from member
minerals alunite, KAl^(SO^)^(OH)^, and beudantite, PbFe^ (AsO^) (SOj^) (OH)^. One member of the latter group, hinsdal- ite, PbAl^CPO^)(SO^)(OH)^, has a composition near to that of
plumbogummite. No X-ray data were available for hinsdalite
and a specimen was sought so that X-ray diffraction studies could be made. The Australian Museum in Sydney kindly don ated a specimen from the original locality of the Golden Fleece Mine, Hinsdale County, Colorado, U.S.A. The diffrac tion patterns of the pseudomorph, plumbogummite and hinsdal ite are given in Table 1 (page 6). From these data it can be seen that the identity of the pseudomorph cannot be re
solved by X-ray diffraction methods alone. Solution of the problem was not attempted at this stage and the line of study was changed to investigate the genesis of the pseudomorph.
By refluxing pyromorphite with a solution of aluminium sul phate, a material yielding a diffraction pattern similar to that of hinsdalite was produced. As a result of this success the writer decided to extend the studies to include the lead bearing members of the Beudantite, Plumbogummite and Alunite Groups. KENSI NGTON £
TABLE 1. Comparison of X-Rav Diffraction Patterns
Hlnsdalite.
Plumbogummite
Dundas A.S.T.M. Card Hinsdalite
Pseudomorph 2-0683 (Colorado)
d d d 1/11 i/q 1/1 1
5-71 95 5.70 80 5.70 92
5-5 8 15 - 5-57 30
4.92 15 4.8V 4o 4.90 3
3-51 60 3-79 40 3-51 44
3.45 20 3.45 60 3-43 18
2.97 100 2.97 100 2.97 100
2.94 10 - 2.93 4
2.86 15 2.82 20 2.85 11
2.79 15 - 2.79 15
2.46 15 2.44 4o 2.45 10
+ In Parts I and II of this thesis only a part of the
diffraction patterns is given. Complete data are
given in Part III - Mineralogical Studies.
The minerals concerned are listed in Table 2 (page 8). In vestigations were planned in three fields, namely mineral synthesis, mineral equilibria and mineralogy.
Mineral syntheses were undertaken to produce the 7 required minerals and other lead bearing compounds of sim ilar structure. It was also planned to examine the possibil ity that other secondary lead minerals, like pyromorphite, were altered by the action of aluminium sulphate.
Studies of mineral equilibria were designed to enable the determination of free energy of formation data which it was thought would allow a more accurate consideration of the alteration of pyromorphite in the presence of aluminium and sulphate ions.
Mineralogical studies were undertaken mainly to obtain
X-ray diffraction data for the minerals concerned since such data have been unavailable up to the present time. Because of the similarity between the diffraction patterns of hins- dalite and plumbogummite, other means of distinguishing these minerals were sought. Chemical spot-testing and differential thermal analysis were thought to be applicable to this prob lem. .8. TABLE 2. Lead Bearing Members of the Alunite.
Plumbogummite and Beudantite Groups.
ALUNITE GROUP
Plumbojarosite PbFe6(S04)lf(0H)12
PLUMBOGUMMITE GROUP
Plumbo gummit e PbAl3(P04)2(0H)?.H20
BEUDANTITE GROUP
Beudantite PbFe3(As04)(S04)(0H)6 Corkite PbFe3(F04)(S04)(0H)6 Hinsdalite PbAl (P04)(S04)(0H)6 Hidalgoite PbAl3(As04)(S04)(0H)6
The minerals concerned have been studied by a number of workers. A chemical classification of the members of the three groups was proposed by Schaller (1911)* Morphological and optical studies of beudantite have been made by Lacroix
(1915)5 of corkite by Miers (1900), of hinsdalite by Larsen and Schaller (1911) and of hidalgoite by Smith et al (1953)* Plumbogummite has been examined by Prior (1900) and plumbo- jarosite by Hillebrand and Penfield (1902) and Hillebrand and Wright (1910)• X-ray data have been published for hid algoite by Smith et al (Op.Cit.). Interplanar spacings and intensities for plumbogummite are listed in the A.S.T.M.
Card Index (Op.Cit.), apparently derived from unpublished 9 records of the British Museum. The cell dimensions and structure of plumbojarosite have been elucidated by Henricks
(1935) and interplanar spacings and intensities have been published by Kauffman et al (1950)* These data have been summarised by Palache et al (1951) and are presented in Table
3 (page 10). The writer wishes to acknowledge the interest shown in the work by his supervisors, Mr. T.K. Hogan, Director of the Broken Hill Division of The University of New South Wales, and Associate Professor L.J. Lawrence of the School of Mining Engineering and Applied Geology, The University of New South Wales. Others at this University to whom acknowledgement must be given include Mr. M. Hatherly and Mr. N.F. Kennon (School of Metallurgy), Dr. N.L. Markham, Dr. F.C. Laughnan,
Mr. G.T. See and Mr. P. Bayliss (School of Mining Engineer ing and Applied Geology). Mr. C.C. Stewart (North Broken
Hill Ltd.), and Mr. M.C. Greaves (Zinc Corporation Ltd.) also gave their advice on a number of occasions. .10. TABLE 3. Available Data for the Lead Members of the Alunite. Plumbogummite and Beudantite Groups.
Morphological Optical Crystallography Crystallography Mineral Axial Axial Refractive Optic Ratio Angle Indices Sign c/a 0 E
Plumbojarosite 4.6667 3#)5' 1.875 1.786 -
Plumbogummite - - 1-653 1.675 +
Beudantite - - - - +3-
Corkite 1.1842 91°161 mean .96 +
Hinsdalite 1.2677 8^40' 1.671 1.689 +
Hidalgoite - - mean 1.713 +
X-Ray Crystallography
c c/a a Space ao 0 arh Group
Plumbojarosite 7.20 33 .60 4.667 11.95 35°C5' R3m
Plumbogummite ------
Beudantite ------
Corkite ------
Hinsdalite ------
Hidalgoite 7.04 16 .99 2.41 6.97 60°43' R3m
3* Palache et al (Op.Cit.p1001) give the optic sign of beu dantite as negative. This appears to be an error since Lacroix (0p.Cit.p36) in the original description gives it as positive. .11.
PART I - MINERAL SYNTHESIS 1. The Alteration of Pyromorphite to Hinsdalite.
Comparison of the formulas of pyromorphite, Pb^CPO^)^
Cl, and hinsdalite, PbAl^CPO^)(SO^)(OH)^, shows that the
ions required for the alteration of pyromorphite are alum
inium, sulphate and hydroxyl. These ions would be available
from a solution of aluminium sulphate and such a solution
could possibly react with pyromorphite in the following manner:
Pb^po^ci + 5ai2(so4)3 + 21H20
PbAl3(P04)(S04)(0H)6 + 2PbS04 + A1(0H)3 + lOHpSO^ + HC1.
5 gms. of pyromorphite, ground to -200 mesh, and 15 gms. Lj. of aluminium sulphate % were placed in a flask with 200 mis. of water and the mixture was refluxed for 24 hours. (Plate 2. page 13) This resulted in a change in the colour of the solids present from the pale yellow of the ground pyromor phite to white. X-ray diffraction study of this material yielded a pattern very similar to that of the Colorado hins dalite. (Table 4, page 12.)
4. The quantities were calculated from the equation to allow approximately 50% excess of aluminium sulphate (AloS04.9H20) in order to force the reaction in the direction of the products. .12. TABLE 4. X-Ray Powder Diffraction Data for the Alteration of Pyromoruhite to Hinsdalite.
...... ■■■■' ...... Pyromorphite A.S.T.M. Card Reaction Hinsdalite
2-0609 Product Colorado d I d I d I
4.31 60 5.70 60 5.70 92
4.09 90 5* 55 10 5.57 30 3-63 20 4.91 10 4.90 3 3-34 60 3* 50 4o 3-51 44
3-24 60 3-46 15 3-43 18
2.95 100 2.97 100 2.97 100
2.86 60 2.93 2 2.93 4
2.2? 5 2.84 5 2.85 11
2.18 20 2.79 5 2.79 15
2.14 10 2.45 10 2.45 10
This pattern is also similar to that of plumbogummite (Table
1, page 6). The problem was noted in the introduction and it is not proposed to deal with its solution in this section.
That hinsdalite was in fact formed in the presence of sul phate and plumbogummite in its absence is demonstrated in the mineralogical section. (page 49.) PLATE 2
Several synthetics in the course of preparation 14.
2. Synthesis of Pyromorphite and Related Minerals. In order that the compounds used in experiments to pro duce members of the Beudantite and Plumbogummite Groups would be of known purity, pyromorphite, mimetite, Pb^CAsO^)^
Cl, and vanadinite, Pb^(VO^)^C1, were first synthesized.
These were produced by refluxing the ortho-phosphate,
-arsenate and -vanadate of lead with an excess of lead chloride. Taking pyromorphite as an example, the equation for the reaction was thought to be as follows: 3Pb (P04)2 + PbCl, JUi 2Pb5(P04)3Cl
The reaction products were examined by X-ray diffraction and in Table 5 (page 16) their patterns are compared with those given in the A.S.T.M. Index for lead ortho-phosphate and pyromorphite. These results indicate that the syntheses were successful. i. Synthesis of Beudantite Group Minerals.
The equation for the alteration of pyromorphite to hinsdalite (page 11) can be written in a more general form as below: Pb^(AOIf)3Cl + 5M2(SOlf)3 + 21H20 ;=?
3PbM3(AOlf)(SOIf)(OH)6 + 2PbS0l+ + A1(0H)3 + lOf^SO^ + HC1
The trivalent ions of aluminium, iron and chromium should be capable of substitution for "N" whilst the quinquevalent ions of phosphorus, arsenic and vanadium can occupy the •Im
position of "A"• An attempt to produce the nine possible
compounds consistent with the various possible substitutions
by refluxing of the required constituents was only partly
successful (Table 6, page 17) • The X-ray data for the products
are given in Table 7 (page 18) where they are compared with
the data for both pyromorphite and hinsdalite.
The attempts to produce the chromium bearing members of
the Beudantite Group, by the refluxing of pyromorphite, mim-
etite and vanadinite with solutions of chromic sulphate were
not successful. The reason for the failure is not certain.
The ionic radius of the chromic ion is very close to that of
ferric iron (O.63A and 0.64A respectively), and hence there
appears to be no crystallochemical reason why it should be
excluded from the lattice. During preliminary synthesis
trials it was observed that the reaction between pyromor
phite and ferric sulphate was far slower than that between
this mineral and aluminium sulphate. This suggests that the
problem may be one of reaction kinetics and that refluxing
for a longer period may effect substitution of the chromic
ion. Alternatively a bomb type synthesis, in which temper
atures and pressures are in excess of those available in an
open vessel, may be required to produce the chromium minerals.
The synthetics containing the vanadate ion, have not yet
been reported as minerals. It is quite possible that they will eventually be found in quartz vein associations as were hinsdalite and hidalgoite or in the oxidized zone of lead ore deposits like corkite and beudantite. TABLE 5* X-Ray Powder Diffraction Data for Pyromorphite. Mimetlte and Vanadinite Synthesis.
Lead Orthophosphate Pyromorphite Pb3(P04)2 Pb^PO^Cl Pb (P0lt)2 + PbCl2 Pb3(As0lf)2 + PbCl? Pb3(V0lf)2 + PbCl2
A.S.T.M. Card 3-0653 A.S.T.M. Card 2-0609 Synthetic Pyromorphite Synthetic Mimetite Synthetic Vanadinite d d d d I/ll d 1/11 I/ll 1/I1 1/I1
4.19 40 4.31 60 4.32 4o 4.4-2 8 4.44 25
4.01 70 4.09 90 4.13 50 4.23 6 4.23 30
3* 58 30 3-63 20 3*66 6 3-73 5 3.83 5 3-30 4o 3-3*+ 60 3-38 , 25 3-44 10 3.68 7 3-16 60 3-24 60 3.27 4o 3.37 40 3.40 40 2.90 100 2.95 100 2.96 100 3-06 100 3.08 100
2.81 70 2.86 60 2.89 70 2.95 25 2.99 85
2.33 0 2.25 5 2.27 6 - - 2.14 30 2.18 20 2.19 15 2.25 45 2.31 5 2.10 20 2.14 10 2.16 8 2.22 3 2.24 7
2.01 40 2.05 80 2.07 35 2.11 10 2.12 25
1.95 4o 1.991 40 1.987 10 1.998 8 1.998 30 1 .92 4o 1.941 70 1.951 20 1 • 966 10 1.968 20
- 1.899 50 1.891 30 1.905 8 1.913 25
1.86 60 1.868 4o 1.865 30 1.865 5 - • 0 0 1.83 0 1.847 70 1.836 15 - £ 7
1.81 60 1.816 10 - - -
1.65 10 1 *669 10 1.677 6 1.680 3 - .17. TABLE 6« Possible Beudantite Group Compounds*
Identity Identity Mineral Result of
of A. of M. Possible Compound Equivalent Synthesis
Phosphorus Aluminium PbAl (P04)(S04)(0H)6 Hinsdalite Successful
Arsenic Aluminium PbAl (As0lf)(S0lf)(0H)6 Hidalgoite Successful
Vanadium Aluminium PbAl3(VOlf)(SOl+)(OH)6 - Successful
Phosphorus Iron PbPe3(P0Lf)(S0lf)(0H)6 Corkite Successful
Arsenic Iron PbFe3(As0lf)(S0lt)(0H)6 Beudantite Successful Vanadium Iron PbFe3(V04)(S0!+)(0H)6 - Successful
Phosphorus Chromium PbCr3(P04)(S04)(0H)6 - Failed
Arsenic Chromium PbCr3(As04)(S04)(0H)6 - Failed
Vanadium Chromium PbCr3(V04)(S04)(0H)6 - Failed . 18. TABLE 7» X-Rav Powder Diffraction Results for Synthetics of the Beudantite Group. *------Hinsdalite M=A1 A=P M=A1 A=As M=A A=V M=Fe A=P M-Fe A=As M=Fe A=V Colorado Hinsdalite Hidalgoite PbAl^(V04)(S04)(0H)6 Corkite Beudantite PbFaj;V04)(S04)(0H)6
d I d I d I d I d I d I d I
5.70 92 68 83 5.73 65 5.74 44 5-95 80 5-97 58 5.99 70
5- 57 30 5-57 36 5-63 23 - - - 5*65 5 - - 4.90 3 4.90 22 4.94 10 4*96 19 ------3-50 44 3.50 50 3-52 65 -- 3*66 35 3.68 31*- 3-69 55 3-45 18 3.45 32 3.48 26 - - 3-51 10 - - - -
2.96 100 2.97 100 2.98 100 3-01 100 3-11 100 3-13 100 3-15 55
2.93 4 2.94 14 - - 2.99 20 3-07 20 3-07 14 3-09 100 2.8? 11 2.8? 18 2.87 8 2.8? 12 ------
2.79 2.79 27 2.81 18 - j - 2.81 20 2.83 12 2.8? 4o 2.45 10 2.46 18 2.47 10 2.48 6 2. ?4 20 2.?? 20 - - Pyromorphite M=Cr A-P M=Cr A=As M=Cr! A=V ASffi Card 2-0609 Synthesis Attempts Not Successful
d I d I d I d I
4.31 60 4.32 40 4.42 8 4.44 25 4.34 60 3.38 40 3-73 5 3-83 5 3-24 60 3.27 40 3.44 10 3.68 7
2.95 100 2.96 100 3-06 100 3.08 100 2*86 60 2.89 70 2-95 25 2.99 8?
2.25 5 2.27 6 2.2? 45 2.24 7 2.18 20 2.19 15 2.11 10 2.12 25 2.14 10 2.16 8 - - - -
2.05 80 2.07 35 - - - - 1 .991 40 1.987 10 1.998 8 1.998 30 19-
4. _Synthesis of Plumbogummite Group Minerals.
Only one member of the Plumbogummite Group, namely plumbogummite, PbAl^CPO^^COH)falls within the scope
of the investigations reported in this thesis. An attempt was made to produce this mineral by refluxing pyromorphite with aluminium acetate. A possible equation for this re action takes the form: 2Pb^(P04)3Cl + 9Al(CH3COO)3 + 18H20 —^
2PbAl3(P0If)2(0H)c..H20 + 7Pb(CH3COO)p + 13CH3COOH + 2HC1.
Syntheses of iron and chromium, 1’analogues” of plumbo gummite, were also attempted by refluxing pyromorphite with the acetates of these metals. The X-ray data for the react ion products of these experiments are presented in Table 8 (page 20). From these data it can be seen that, as in the case of the Beudantite Group minerals, synthesis of the alum inium and iron bearing compounds was successful, but the attempt at substitution of the chromic ion failed.
5. Alteration of Secondary Lead Minerals.
The marked effect of aluminium bearing solutions on pyromorphite and related minerals suggested that such sol utions may have some effect upon other secondary lead min erals .
To examine this possibility samples of anglesite, PbSO^, cerussite, PbCO^, crocoite, PbCrO^, stolzite, PbWO^, and 20
TABLE 8. X-Rav Powder Diffraction Results for Synthetic Plumbogummite and Related Compounds*
Pyromorphite Plumbo gummit e Pb?(P01+)3Cl + A1(CH3C00)3 Pb?(P04) Cl + Fe(CH3C00) Pb?(P04) Cl + Cr(CH3C00)3
A.S.T.M. Card 2-0609 A.S.T.M. Card 2-0683 PbAl3(P04)2(0H)5.H20 PbFe3(P04),(0H)4.H20 No Reaction
d I d I d I d I d I
4.31 60 5.70 80 5.72 20 5-97 30 4.34 4o
4.13 50 - - 5*59 10 - - 4.14 50
3*66 6 4.84 4o 4.93 5 - - 3.68 5
3-38 25 3-79 4o 3.51 10 3*68 10 3*39 35 3-27 40 3.45 60 3.46 6 3-53 3 3*27 45
2.96 100 2.97 100 2.98 100 3*12 100 2.96 100
2.89 70 - - - - 3-07 15 2.89 90
2.27 6 2.82 20 2.88 20 - - 2.27 ?
- 2.80 6 2.81 10 2.20 2.19 15 A 15 2.16 8 2 • 44 40 2.47 4 2.54 5 I 2.17 10 .21 . wulfenite, PbMoC^, were refluxed in solutions of aluminium
sulphate. The products were examined by X-ray diffraction
and the results are given in Table 9 (page 22). Anglesite and crocoite remained stable throughout the period of reflux
ing whilst cerussite and stolzite were converted to angle-
site. Wulfenite exhibited fair stability although weak angle-
site reflections were recorded, indicating that reaction with the aluminium sulphate had commenced. There has apparently
been no tendency towards the production of equivalents of plumbojarosite, containing aluminium and the various divalent anions. 22
TABLE 9. X-Rav Diffraction Data for Reaction Products from Reaction between Various Secondary Lead Minerals
and Aluminium Sulphate.
PbCO^ + PbW04 + PbMoO^ +
Anglesite PbSO^ + Cerussite Al9(S0If)3 Crocite PbCr04 + Stolzite ai?(so4)3 WuIfenite ai9(so4)3
ASTM Card A12(S04)3 ASTM Card Compare with ASTM Card ai2(so4)3 ASTM Card Compare with AS TM Card Slight Reaction +
5-0577 No Reaction 5-0417 Anglesite 8-209 No Reaction 8-476 Anglesite 8-475 Anglesite Lines
d I d I d I d I d I d I d I d I d I d I
5-3 8 3 - - 4.427 17 - - 5-43 10 5.42 7 3-252 100 5-36 3 4.96 11 4.99 12
>+.26 87 4.24 90 4.255 7 4.15 60 5.10 6 5* 06 10 3-014 22 4.25 65 3- 244 100 4.26+ 3
3-813 57 3-80 40 3-593 100 3-81 4o 4.96 25 4.95 25 2.732 32 3-82 4o 3- 028 22 3-82+ 2
3-622 23 3-62 35 3.498 43 3-62 20 4.38 25 4.37 20 2.394 1 3-62 20 2. “718 24 3.47+ 3
3-479 33 3-49 55 3-074 24 3-49 30 3-76 12 3-76 10 2.024 35 3.48 20 2. ^83 8 3-32+ 4
3-333 86 3*33 85 2.893 2 3-33 100 3-72 7 3-72 10 1.9309 16 3-33 100 2. 212 5 3-25 100
3-220 71 3-21 90 2.644 2 3-22 45 3-48 55 3-48 30 1.8377 <1 3-21 50 2. 382 7 3-02 20
3-001 100 3-00 100 2.589 11 3.01 80 3-28 100 3-27 100 1.7817 21 3.00 65 2. 321 31 3.00+ 10
•2.773 35 2-767 35 2. 522 20 2.767 25 3-15 11 3-14 10 1•6603 33 2.76 20 1 . 787 18 2.720 20
2.699 46 2.698 30 2.487 32 2.699 30 3.09 6 3-09 7 1.6255 16 2.699 30 1 . S53 25 2.21 5 5 •23.
PART II - STUDIES OF MINERAL EQUILIBRIA.
This section is concerned largely with attempts to ob tain some physico-chemical data of use in the study of the formation of hinsdalite and corkite from pyromorphite. By determining the equilibrium concentration of ions in a solut ion in contact with the solid mineral, it is possible to arrive at the free energy of formation of that mineral. This is achieved by first determining the solubility products of the mineral at various ionic strengthsand extrapolating these values to infinite dilution to yield the value of the equilibrium constant. From this the free energy of formation of the mineral can be calculated. The theoretical basis for this approach to the problem is briefly discussed below. Detailed discussion of the principles involved are to be found in most text books of physical chemistry such as Glass- tone (1951) and an excellent summary treatment of the subject is given by Garrels (i960).
5* The ionic strength 'V' of a solution is a function of both the concentration and charge of the ions present. It has been found to give more consistent results for the effects of electrolytes on such properties as the solubility of solids than does concentration alone. Its value is given by the relationship M- = ^-Scz^ where "cM is the concentration of the ion and "z" is its charge. .24.
1. The Solubility Product -Equilibrium Constant Relationship
The determination of the equilibrium constant Mkn for a reaction in which a mineral comes to equilibrium with a solution of its constituent ions, can be approached by means of solubility studies. For a mineral X.^+ ^2^” in equilibrium with a solution of its ions, it follows that: X,Y2Z *=5 3X2+ + 2Y2" + Z2_.
The solubility product MKM for the mineral is given by the equation:
K=(m0.)3(m9)^(m9) ...(1) Z^“ where nmn is the concentration of the ions present expressed
6 • in terms of molality . The equilibrium constant for the dissociation of the mineral into its ions is given by the equation:
k = (a 9.)^(a 9 )2(a 0 ) ... (2) XT Z^~ where "a" is the activity of the constituent ions. The
6. The molality of a constituent is given by: _ weight of solute x 1000______formula weight of solute x weight of water. The weight of water in this relationship is often re placed by the volume of solution. Strictly speaking use of the latter gives the molality "M" although the difference is small provided that the solution is dilute. 25- relationship between the concentration and activity of an ion is:
m (3) where 'V is known as the activity coefficient. Substit ution of equation (3) in (1) yields the following:
r2+ \3 -2-\2 ,2- • • • (4) r2 + r2- -2- and this equation may be combined with equation (2) to give:
k — K( 2+) ^ 2- ^ 2-* ... (5) X Y Z
Since the ion activity coefficients approach unity at in finite dilution, extrapolation of the solubility product to zero ionic strength will give the value of the equilibrium constant. The relationship between the activity coefficients of a given ion and the ionic strength of the solution in which it occurs is given by the Debye-Huckel Theory. In dilute sol utions the relationship takes the form:
log y = • (6) 1+gB/jI where "A" and MBn are constants characteristic of the sol vent at particular temperatures and pressures, Mz" is the valence of the ion under consideration, 1V is the ionic strength and Ma" is a value related to the effective diameter of the ion in solution. Applying equation (6) to the mineral considered above, there results: .26. -4Avu log # P+ . . . (7) Yr 1 +§B/jI -4a 41 log # p . . . (8) 1 +aB/q -4A 4x log 6 p . . . (9) Zd 1+aB/iI
If logs are taken of both sides of equation (5) and the values of the log# terms from equations (7) - (9) are sub stituted, there results:
log k = log K - 3(—'o^ -) J ^ ) • • • (10) 1+aB/jj. 1+aB/jI 1+aB/jI
At very low ionic strengths the denominators on the right of the equation approach unity and hence equation (10) becomes:
log k = log K - 24A/jit . . . (11)
At 2‘?°C, A is 0.5085^* and hence equation (11) can be written approximately as:
log k 2 log K - 12Jjl . . . (12)
It can be seen that an equation of the form of (12) is ex tremely valuable in the extrapolation of the solubility pro ducts to infinite dilution. It shows that the solubility product is a linear function of the square root of the ionic strength, and that the limiting gradient is -12.
7* Garrels (Op.Cit. P. 29)• .27.
2. Equilibrium Studies of Hinsdalite Formation.
The theory outlined above was applied to the formation
of hinsdalite by allowing varying amounts of lead ortho phosphate in solutions of aluminium sulphate to come to equi
librium. The small amounts of lead phosphate required were obtained by adding a solution of sodium hydrogen phosphate
to one of lead nitrate. Aluminium sulphate was then added
in sufficient quantity to allow conversion of the lead phos phate to hinsdalite. The reactions taking place were thought to be:
(1) 3Pb(N03)p + 2NaHP01+ ^ Pb^PO^ + 4NaN0^ + 2HN03
(2) Pb3(P04)2 + 3A12(S04)3 + 12H20
2PbAl3(P04)(S04)(0H)6 + PbS04 + 6H2S04.
The maximum concentration of lead nitrate used was 0.012M and the total volume in which reaction was to take place was
50 ml. Based upon these limitations the concentrations of the standard solutions were found as follows:
Desired
Concentration gm./1000ml. gm./50ml.
0.012M Pb(N03)2 331.23 x 0.012 = 3*9748 0.1987
0.008M NaHP04 141.97 x 0.008 = 1.1358 0.0568
0.012M Alp(S04)3.9H20 504.28 x 0.012 = 6.0514 0.3026
In order that these quantities could be added to yield a total volume of 50 mis. for the most concentrated solution, .28. the standard solutions were made up at the following concen trations :
Pb(N0^)p - O.I987 gm./40 mis. NaHPO^ - 0.0568 gm./4 mis.
Alp(S0If)^.9Hp0 - 0.3026 gm./4 mis.
From these standards, triplicated "reactant" solutions were made up by adding the quantities given in Table 10 below, to
50 ml. volumetric flasks which were made up to volume with distilled water.
TABLE 10. Reactant Solution Composition for Hinsdalite
Equilibrium Study.
Soln. Pb(N03)2 Na, ai2(so4) ,9H20 »hpo4 No. ml. gm. ml. gm. ml. gm.
1 40 0.1947 4 0.0568 4 0.3026
2 30 0.1491 3 0.0426 3 0.2269 3 20 0.0994 2 0.0284 2 0.1513
4 10 0.0497 1 0.0142 1 0.0757 r- The contents of the twelve flasks were kept approximately at 25°C for six months to allow the attainment of equilibrium. The constant temperature bath was probably a unique, if some what undignified, piece of apparatus. As there was no temp erature bath in Broken Hill that could be stabilized at 25°C it was decided to store the flasks underground where the temperature fluctuates less than at the surface. Discussions .29* with the ventilation engineers of North Broken Hill Ltd.,
revealed that the temperature record for the worked out 1100
ft. level of this company's mine was approximately constant
at 25°C. The flasks were therefore sealed in a box and placed
in a remote part of the level. Agitation of the flasks was
achieved by fitting the box with a pully which was linked to
the drive shaft of an air-motor, enabling the box to be turned
end for end.
After the six months had elapsed the solutions were fil
tered and analysed. Only brief reference is made to the
analytical procedures here as the details are given in the
Appendix (page 1(W. The pH was measured by use of a Leeds
and Northrup pH meter. Aluminium was determined colorimet-
ricly (8-hydroxyquinoline), lead by polarography, phosphate
colorimetricly (molybdophosphoric acid) and sulphate by tur-
bidimetry. The averaged analytical data for the solutions
are given in Table 11 (page 30). In this table the upper
figures give the amounts of ion present in mg. whilst the
lower figures give the molality of the ion, except in the
case of the hydroxyl ion, for which the figures refer to pH
and activity.
For each solution the solubility product for hinsdal-
ite and the ionic strength were calculated as shown in the
example (Solution 1) page 31* 30
TABLE 11. Averaged Analytical Data for Hinsdalite Equilibrium Study.
Solution 1 Solution 2 Solution 3 Solution 4
Aluminium
17-9 12.5 8.60 2.75 0.013280 0.009255 0.006000 0.002200 Lead
1.10 1.50 1.55 1.60 0.000106 0.000145 0.000150 0.000154 Phosphate
4.34 2.75 1.65 0.68 0.000914 0.000578 0.000344 0.000143 Sulphate
16.35 12.00 8.20 3-90 0.003400 0.002500 0.001708 0.000812 Hydroxyl
2.82 2.88 2.96 3-14 k k 1 • -r __ — 10-H.12 0 1q-10.86
10-11,18 0
Sodium +
16.3 12.4 8.2 4.1 0.0141 ?o 0.010610 0.007075 0.003538 Nitrate +
74.4 55* 8 37.2 18.6 0.011990 0.008993 0.005995 0.002998
+ These ions not determined, quantities present known from original standard solutions • •31. Solubility Product
K = (m 0+)(m 3+)^(m o )(m o )(m Pb^ A1J P04J" S0^“ 0H“
. log K = log 0.000106 + 3 log 0.013280 + log 0.00091*+
+ log 0.003400 - 5.18 log 10
= -(3.97^69 + 5.6304-3 + 3.03905 + 2.46852 + 5-18) = -20.29 •
Ionic Strength 2 U — -g-2cz
= i[(0.000106 x 4) + (0.013280 x 9) + (0.000914
x 9) + (0.003400 x 4) + (0.014150) + (0.011990)]
= 0.083955 .'./£ = 0.290
These calculations were repeated for solutions 2-4 and the data so obtained are recorded in Table 12, below.
TABLE 12. Log K and /u Values for Hinsdalite Reactant
Solutions.
1 2 3 4
Log K -20.29 -20.90 -21.76 -23.58
0.290 0.245 0.197 0.125
By plotting the variation of log K with /jl and extra polating the resulting line to zero ionic strength a value for the logarithm of the equilibrium constant is obtained. •32.
To aid the extrapolation, use is made of the Debye-Huckel
Theory as shown on page 25* Hence for hinsdalite:
PbAl3(P04)(S04)(0H)6
log k = log K - (4a;(jl) - 3(9A/mJ - (9A/u) - <4a^)
= log K - 44A/p,
at 25°C A = 0.5085
log k = log K - 22yjjL*
This shows that the limiting gradient between log K and f\L in the case of hinsdalite is -22. It is also to be noted that no term appears for the hydroxyl ion since the activity
"a" of this ion is known and it is cancelled at the stage of combining equations 2 and 4 (pages 24, 25) to relate the solubility product and the equilibrium constant.
The graph of log K against /jl is shown in Figure 1 ,
(page 33) and extrapolation of this to zero ionic strength shows the logarithm of the equilibrium constant to be -26.1.
Hence for the dissociation of hinsdalite into its constit uent ions:
PbAl3(P0lf)(S0lt)(0H)6 Pb2+ + 3A13+ + PO^3' + SO+ 60H' p/ -J the equilibrium constant is 10”
The change in standard free energy in a reaction is rel ated to the equilibrium constant as follows:
AFr° = -RT In k ... (13) where MRM is the gas constant and "TM the absolute temperature 33
Figure 1. Determination of Equilibrium Constant for Hinsdalite Reaction. •34.
At one atmosphere pressure and 25°C, R = 0.00198 k.cal/deg. and T = 298.16 deg. Substituting these values in the above equation and changing the logarithm to the base 10, there results:
AF° = -1.364 log k k.cal. . . . (14)
Applying this to the dissociation of hinsdalite:
AFr° = -1.364 X -26.1
= 35.6 k.cal.
Since the values for the free energies of formation, from theirg elements, of the constituent ions of hinsdalite are known *, the above value enables the calculation of the free energy of formation of hinsdalite as follows:
For any reaction
AFR° = ^Products - ^Reactants • • • 05) and from the dissociation reaction for hinsdalite: ,0 2AF (AF°b2+ + 3 = -(5.81 + 345.00 + 245.10 + 177.34 + 225.54) - 35-6 = -1034.4 k.cal. 8. Handbook of Chemistry and Physics, 43rd Ed. (1961) pp 1882 - 1918. •3? Equilibrium Studies of Corkite Formation. The procedures and calculations applied to the hins- dalite study were repeated for corkite, the reactant solut ions varying only in the substitution of ferric sulphate for aluminium sulphate. The composition of these solutions is given in Table 13, below. TABLE 1Reactant Solution Composition for Corkite Equilibrium Study. Soln. Pb(NO )2 Fe2(S04)3 Na,>HP04 No. ml. mg. ml. mg. ml. mg. 1 4o 0.1947 4 0.0568 4 0.2399 2 30 0.1491 3 0.0426 3 0.1799 3 20 0.0994 2 0.0284 2 0.1200 4 10 0.0497 1 0.0142 1 0.0600 The solutions were analysed after six months. Ferric iron was determined colorimetricly by the use of a blue com plex with catechol. This is a new procedure for iron devel oped by the writer during the course of the present studies and it is described in the Appendix. The other ions were determined as in the case of hinsdalite. The averaged analytical data is given in Table 14 (page 36.), whilst the details are recorded in the Appendix. TABLE 14. Averaged Analytical Data for Corklte Equilibrium Study* Solution 1 Solution 2 Solution 3 Solution 4 Iron 18.5 11.5 5.4 2.4 0.006700 0.004100 0.001928 0.000857 Lead 0.75 0.65 0.55 0.45 0.000072 0.000063 0.000053 0.000043 Phosphate 3-33 1.80 0.87 0.30 0.000701 0.000379 0.000183 0.000063 Sulphate 14.9 11.10 5.90 2.20 0.003100 0.002310 0.001230 0.000458 Hydroxyl 1*33 1.63 2.08 2.82 10-12.67 10-12.37 10-11-92 10-H.18 Sodium + 16.3 12.4 8.2 4.1 0.0141 50 0.010610 0.007075 0.003538 Nitrate + 74.4 55- 8 37-2 18.6 0.011990 O.OO8993 0.005995 0.002998 + These ions not determined, quantities present known from original standard solutions. •37. The solubility products and ionic strengths of the sol utions computed from the averaged analytical data are given in Table 15, below. TABLE 15. Lor K and 7u Values for Corkite Reactant Solutions. 1 2 3 4 log K -23.0 -23.79 -24.99 -26.29 A 0.230 0.187 0.137 0.092 Application of the Debye-Huckel Theory to obtain the limiting gradient for the graph of log K versus J\i for corkite, yields the same value as for hinsdalite, namely -22. The graph is shown in Figure 2 (page 38) , and extrapolation to zero ionic strength gives a value for the equilibrium constant for dis- sociation of corkite of 10” * . Substitution of this value in equation (14), page 34, yields the free energy of dissociation for corkite: o afr = -1*364 log k k.cal. = -1.364 x -28.1 = 36.4 k.cal. • 38. Figure . oterminalion of 'quillbrlu.-: Cons tant for CerH t ^ Keact i. r.. -39- The dissociation reaction for corkite is: PbFe3(P0lf)(S0l+)(0H)6 ^=i Pb2+ + 3Fe3+ + PO^- + SO^2" + 60H' and thus from equation 0 5) page 3*+? ^Reactants = AFPb2+ + 3 = -(5.81 + 7 . 59 + 245.10 + 177-34 + 22 5-54) -(38.4) = -699-8 k.cal. 4. Equilibrium Studies of Pyromorphite Formation. Determination of the equilibrium constant for the dis sociation of pyromorphite into its constituent ions was made in a similar manner to the determinations for hinsdalite and corkite. In this case sodium hydrogen phosphate was added to a solution containing lead chloride, in slight excess over the amount that would be precipitated by the phosphate. Reaction between the precipitated lead phosphate and the lead chloride in solution gives rise to pyromorphite as follows: 3PbCl2 + 2Na9HP04 ^==? Ph^PO^) ? + 4NaCl + 2HC1 3Pb3(P0lf)2 + PbCl2 =e 2Pb^(P04)3Cl or combining these: 278.12 141.08 10PbCl9 + 6Na2HP01+2Pb^(P0)+) Cl + 1 2NaCl + 6HC1 .40. From the equation it follows that 2?81 gms. of lead chloride require 847 gms. of sodium hydrogen phosphate for precipitation and conversion to pvromorphite. This reduces to 1 gm. of lead chloride requiring 0*3039 gm. of the phosph ate. Accordingly^ standard solutions of 5*02 gms. PbClp/500 mis. (allowing a slight excess over requirements) and of 3*0393 gms. ^2^0^/200 mis. were made up. Reactant solut ions of various concentrations were prepared from these and each was bulked to 200 mis. in a volumetric flask. As in the case with the earlier studies the solutions were made up in triplicate. The compositions are given in Table 16. TABLE 16. Reactant Solutions Composition for Pvro morphite Equilibrium Study. Soln. Na PbC12 2HP°4 No. ml. gm. ml. gm. 1 100 1.0040 20 0.3039 2 75 0.7530 15 0.2279 3 50 0.5020 10 0.1519 4 25 0.2510 5 0.0759 The reactant vessels were stored as before to allow the establishment of equilibrium. Unfortunately at this stage the writer was notified by his employers that he was required to move to North Queensland. As a result the reactant sol utions had to be analysed only a month after preparation. Ihis was possibly too short a time to allow complete attain- .41. ment of equilibrium. The analytical procedures were as for hinsdalite and corkite although the phosphate concentration was found to be very low and a new calibration curve had to be drawn up to cover a lower range. Chloride was present in consider able concentration and was determined by volumetric means. The averaged analytical results are given in Table 17, below, and the details are set out in the Appendix. TABLE 17. Averaged Analytical Data for Fyro- mornhite Equilibrium Study. Solution 1 Solution 2 Solution 3 Solution 4 Lead 35-2 29.4 26.1 23-4 0.000850 0.000710 0.000630 0.000587 Phosphate 0.85 0.62 0.55 0.41 0.0000448 0.0000326 0.0000290 0.0000216 Chloride 221.5 168.2 115.1 62.1 0.03118 0.02368 0.01642 O.OO887 Sodium + 98.5 74.4 49.2 24.6 0.0214o 0.01605 0.01070 0.00 53? + This ion not determined, quantity present known from original standard solutions. .42. From the analytical data the solubility products for pyromorphite and the ionic strengths of the reactant solut ions were calculated and the results are given in Table 18. TABLE 18. Log K and Vu, Values for Pvromornhite Reactant Solutions. Soln. No. 1 2 3 4 log K -29.91 -30.73 -31.40 -32.21 fM 0.168 0.146 0.122 0.090 From the graph of log K versus J\L (Figure 3? page 43) the average gradient was found to be approximately -30 where as Debye-Hiickel theory shows that it should be -24. This deviation is possibly due to the failure of the system to come completely to equilibrium. If this is the case then it is reasonable to assume that the solution of lowest ionic strength will be nearer to equilibrium than that of highest ionic strength. Closer inspection of the array of points supports this view since they do in fact lie on a curve which becomes assymtotic to a line at the theoretical gradient placed just above the plot of data for the least concentrated solution. The line gives an intersection at infinite dilut ion of -34.5 and this value should closely approach the true value of log K. For the dissociation: Pb^CPO^) Cl ^ 5Pb2+ + 3P0^- + Cl" -36 -35 ■ Figure 1. Determination of Equilibrium Constant for Pyromorphite Reaction. .44. _ oLj.# p the equilibrium constant k is 10 J and using this value to obtain the free energy of dissociation for pyromorphite: AFr° = -1.364 log k = -1.364 x -34.5 = 47*1 k.cal. Furthermore for the dissociation reaction: ^^Products ” ^^Reactants o • • AF Reactants (5AF£b2+ + 3AFp0lf3- + ^ci-5 * 47>1 -(29.05 + 753.30 + 31.35) - 47.1 = -842.8 k.cal. The possible variation in the value of -log k, permitted by the deviation of the reactant solutions from equilibrium only amounts to about a k.cal. This would produce less than 0.2$ variation in the free energy of formation of pyromorphite. CT. Application of Free Energy Data to the Alteration of Pyromorphite. In the mineral synthesis section it was proposed that the equation for the formation of hinsdalite from pyromorphite may have been: • *+5. -842.3 -759*3 -56-7 Pb^-(p°i+) 3C1 + 5A12(S04)3 + 21H20 -1034.5 -271.9 -193-9 -177.3 -31.^ ,=+ 3PbAl,(P0lf)(S0i+)(0H)6 + A1(0H)3 + 2PbS01+ + lO^SO^ + HC1 . Using equation (15”) above to find the free energy change involved in this reaction: AFr° = 2AFproducts - ^Reactants = -(3103.5 + 271-9 + 387.8 + 1773*1+ + 31 • *+) +(842.3 + 3796.5 + 1190.7) = -5568.4 + 5829.5 = +261.1 k.cal. From this it is seen that the reaction proposed results in an increase in the free energy of the system and thus it cannot take place spontaneously. In the initial attempt to find an equation which could explain the natural alteration of pyromorphite to hinsdalite, the fact that the former mineral occurs as a pseudomorph, was not utilized. This fact places a volume restriction on the equation as the original volume of each pyromorphite crystal must remain virtually unchanged by the reaction. The relative volumes occupied by the two minerals are obtainable from the X-ray diffraction results. Pyromorphite crystallises in the hexagonal system and its cell dimensions are aQ = 9-97A and cQ = 7-32A (A.S.T.M. Card 8-103). Al though hinsdalite crystallises in the rhombohedral system it • 46 • can be referred to a hexagonal cell (triply primitive) which is convenient for the present purpose of comparison. For the hexagonal cell of hinsdalite aQ = 7*00 and cQ = 16.72 (From Mineralogical Studies, page 62-). These values give volumes of the pyromorphite and hins dalite cells as 630A^ and 71OA^ respectively. By a trial and error process the ratio of the number of cells of each mineral which would give approximately equal volumes was sought. For pyromorphite : hinsdalite this was found to be 9:8, equivalent to volumes of 5670A^ and 5690A-3 respect ively. From the fact that the hinsdalite cell is triply primitive, that is it contains three molecules, the above ratio shows that for a constant volume reaction, 9 molecules of pyromorphite must give rise to 24 molecules of hinsdalite. A reaction based upon these values is: -842.3 -115*0 -177*4 -37*6 9Pbj(PC>4) ,C1 + 72A13+ + 24S02- + 1440H-(+24Cl~) ;=* -1034.4 -5.8 -24J.1 -31.4 24PbAl (P0lf)(S04)(0H)6 + 21Pb2+ + 3P0^‘ + 9c1-(+24C1-) As there is no knowledge of the composition of the solution carrying the reactant ions, nor of products, other than hins dalite, which may have been formed by their reaction with pyromorphite, the equation is written in an ionic form. The chloride ions included in brackets serve no other purpose than to create electrical neutrality on either side of the equation and they cancel each other in free energy consider ations . .47. As before the free energy change accompanying the reaction is given by: = Products - ^Reactants. = -(24820.2 + 121.8 + 735-3 + 282.6) +(7586.1 + 8280.0 + 4257*6 + 5414.4) = -25959.9 + 25538.1 = -421.8 k.cal. This value shows that a decrease in free energy accom panies the change of pyromorphite to hinsdalite and thus the process can occur spontaneously. As this is what would be required for the genesis of hinsdalite in the oxidation en vironment, and furthermore since the revised reaction is at constant volume, it is quite possible that alteration of pyromorphite took place as indicated in the equation on page 46. An equation similar to that above can be written for the alteration of pyromorphite to corkite: -81+2.3 -2-5 -177-4 -37.6 9Pb[.(P01+) ^Cl + 72Fe3+ + 24S042~ + 1440H“(+24C1") ;—* 699-8 -5-8 -245-1 24PbFe3(P0lf)(S0lt)(0H)6 + 21Pb2+ + 3P01+3- + 9Cl‘(+24Cl“) Substituting these data in the free energy equation: .48. o EAF Products Reactants = -(16789.8 + 121.8 + 735.3 + 282.6) + (7586.1 + 180.0 + 4257.6 + 5414.4) = -17929-5 + 17438.1 = -491.4 k.cal. As with the alteration to hinsdalite, the decrease in free energy accompanying the alteration of pyromorphite to corkite shows that the reaction could take place spontan eously. Palache et al (Op.Cit. p 1002) record the occurr ence of corkite in the oxidised zone of lead deposits, but there appears to be no record of the mineral replacing pyro morphite. The origin of pyromorphite in the oxidised zone places it in an environment generally rich in ferric iron and its failure to react with this may well be a kinetic problem. At surface temperatures the reaction may be infinitely slow and under these conditions the pyromorphite is essentially stable in the presence of ferric iron. .49. PART III - MINERALOGICAL STUDIES The fine grained nature of the synthetic materials pre cluded microscopic examination, and as a result the studies were undertaken by means of X-ray powder diffraction. Hins- dalite was the only member of the Beudantite Group available for use as a reference material. This was subjected to a precise study to allow the determination of a large range of interplanar spacings and several of these were selected for the calculation of the unit cell constants for the mineral. The study of the synthetics was limited to the minimum nec essary to enable the unit cell calculations. 1. X-Rav Diffraction Studies of Colorado Hinsdalite. For the initial study the powdered mineral was examined by means of a Phillips Model 1050 X-Ray Diffractometer at a scanning rate of degree per minute and a rate-meter setting of 16. The interplanar spacings computed from the resulting diffractometer trace are given in Table 19 (pages 50, 51) • The 29 values were readily obtainable to an accuracy of t 0.05 degrees. The intensities of the diffractions were obtained by measuring the areas under the respective peaks of the dif fractometer trace and then adjusting these to give the strongest a value of 100. An algebraic method was used to index the diffraction pattern. This required the identification of a number of • 5o. TABLE 19. Internlanar Spacings for Colorado Hlnsdalite. 2© d ^1 2© d 1/11 15- 55 5.70 92 62.25a 1.491 4 1 § 15.90 5.57 30 62.70 • 22 18.10 4.90 3 63-45 1.466 24 25.50 3.49 44 65* 50 1.426 4 25.85 3.45 18 67-20 1.392 3 30.20 2.96 100 68.25 1-373 4 30.50 2.93 4 66.60ai 1 • 366 8 31.50 2.848 11 69-55 1-351 6 32.10 2.788 15 71.30 1.321 3 36.65 2.452 20 72.90 1-295 7 39.70 2.270 73-60 1.286 8 9 40.10 2.258 12 75.45 1.258 8 4o. 55 2.224 86 79.80 1.201 10 4o. 80 2.211 17 81.10 1.185 8 51-35 2.183 15 82.05 1.175 3 44*90 2.018 2 84.30 1.148 1 45.10 2.010 10 84.90 1.141 2 45.85 1.978 9 86.70 1.123 6 47.90 1.899 36 92.85 1.064 3 49.05 1.857 1 96.55 1.033 4 52.25 1.751 16 97.85 1 .021 2 • 51- TABLE 19. Interplanar Spacings for Colorado Hinsdalite. Cont'd. 2© d I/ll 2© d I/I-, 53-1? 1.722 8 99-55 1 .010 1 55-05 1 • 668 4 100.25 1.005 1 55* 50 1.655 11 102.30 0.989 7 55-95a: 1.642 29 105.00 0.972 4 CO 57-00a 1.614 108.55 0.950 3 j- 61.75 1.503 key spacings from which aQ and then cQ could be calculated. Once these values were found they were used to compile a table of possible interplanar spacings which was compared with the set recorded from the diffractomer trace. Previous work by Henricks (Op.Cit. p. 781) has shown that minerals of the Beudantite Group crystallize with rhom- bohedral symmetry. Computations for such materials are usually carried out by first assuming hexagonal symmetry and then transforming these results into the rhombohedral frame work. The equation for hexagonal symmetry may be written: ,2 _ Mil2 + hk + k2) . 12n-1 ‘hkl " ( ~2 + ~2> . . . (1) 3a c For planes which parallel the c direction 1=0 and the equation becomes: 2 dhk0 = (where % = h2 + hk + k2) . . . (2) H From the data recorded by Palache et al (Op.Cit. p.1004) it is apparent that for minerals of the Beudantite Group the value of aQ is approximately 7* Limiting the spacings to those whose reflections are reasonably strong, reference to Table 19 shows that the smallest spacing that need be consid ered is 1.466A. (I/I^ = 24). Substitution of these limiting values in equation (2) shows that the upper permissable value for Ng is 16 (hkO = 400). A further limitation may be placed upon the values of because of the rhombohedral symmetry. •53- In a crystal with a rhombohedral lattice which has been re ferred to hexagonal axes, spacings for which the condition -h + k + 1 = 3n (where n = 0, 1, 2, 3> • •••) is not fulfilled, do nob occur. Hence of the values of between 1 and 16 per mitted by hexagonal symmetry, only those of 3? 9? and 12 are acceptable in this instance. These values were substituted in equation (2) and the resulting spacings sought in Table 19. The data obtained by this procedure are recorded in Table 20. TABLE 20. Preliminary Data for the Calculation of a . hkO 2© 1/I1 kh ^calc ^obs 3 110 3*5oo 3-51 25*50 44 9 300 2.020 2.018 44.90 2 12 220 1.749 1.752 52.25 16 Of these spacings only those of (110) and (220) have sufficient intensity to be of use in the accurate determin ation of a • The 2© values corresponding to these spacings were established with greater accuracy by taking fixed counts at 2© intervals of 0.01 degrees (Table 21, page Jb) and using these results to contour the diffracted beam (Figure 4, page 55)- This enabled 2© to be measured with an accuracy of at least 1 0.01 degrees. From the values so obtained the res pective interplanar spacings were found to be 3*50 and 1.750. Together with their indices these were substituted in equation (2) to obtain the value of a • These data are given in Table 22 (page 56) and show that the value of aQ is 7*00A. In retrospect, such a value could have been anticipated from the close agreement between the observed spacings and those calculated on the assumed value of 7 for a • Further reference to Palache et al (Op.Cit. p. 1004) shows that the value of cQ to be expected for hinsdalite is approximately 17* Equation (1) for the hexagonal system can be recast as: _J__ 2 (3) dhki c Substitution of the value for aQ in this equation yields the following: 1____ ,2 = 0.02721 Nr + ... (4) dhkl c TABLE 21. Fixed Count Data for Determination of 29. d * 3.49 25.44 • 45 .46 • 47 .48 .49 •50 29 Time (sec) 20.2 18.6 17.8 17.6 17.8 19*4 20.9 RM 64 d - 1.752 52.27 .28 .29 •30 •31 •32 •33 • 3^ 29 Time (sec) 25.0 22.6 21.5 20.8 21.4 22.4 23.8 24.9 RM 32 •55 FliTure 4. Line Contours frotr Fixed Count Data. TABLE 22. Data for Determination of a > 29 d d2 hk.O a 2 nh ao ao 2?.k7+ 3-50 12.250 11.0 3 49.00 7.00 52.30 1.750 3-063 22.0 12 49.01 7.00 + A variation of t 0.01 degrees in 29 produces a variation of less than t 0.01 in the length of a • Some of the more strongly diffracting planes were sel ected for the calculation of c • Assignment of indices to these planes was carried out by trial and error utilizing p equation (4). For each spacing various values of and 1~ i were substituted in the equation until a value of — of approx- c imately 0.0035 was obtained. The spacings selected from Table 19 (page 51) for the application of this procedure were 2.96, 2.788 and 1.899* The results of substitution of these values together with their assigned indices are given in Table 23. TABLE 23. Preliminary Data for Calculation of c ♦ 1 l2 1 d( A) hk.l 0.0272NH 2 2 d2 c c 9 2.96 0.1141 0.0816 0.0036 11.3 0.0325 36 2.788 0.1287 00.6 0.0036 0.1287 9 1.899 0.2773 30.3 0.2448 0.0036 0.0325 57- As in the case of computation of the value aQ the res pective values of 29 were accurately established by taking fixed counts. These data are recorded in Table 24 below. By using the more accurate 29 data and repeating the proced ure shown above, the value of cQ was found to be 16.72A. The results are given in Table 25, below. TABLE 24. Fixed Count Data for Determination of 29. d - 2.96 30.12 .14 • 16 .18 29 .13 .15 •17 Time (sec) 17.8 16.4 1 5.8 15.5 16.1 • 16.7 17.2 rm 128 j*------d * 2.788 .11 .14 29 32.09 .10 .12 .13 .15 Time (see) 17.4 15.8 RM 128 16.1 15.6 16.0 16 • 8 18.0 d - 1.899 00 OO CO 0. • • 00 47.85 ON .89 29 .90 .91 Time (sec) 12.0 11.0 12.4 RM 32 13-3 11.3 11.5 13-6 TABLE 25. Data for Determination of c . 29 d 1/d2 hk.l 0.0272Nr l2/c2 'o2 co 30.15+ 2.964 0.1138 11.3 0.0816 9/0.0322 279.5 16.72 32.12 2.787 0.1287 00.6 - 36/0.1287 279-7 16.72 47.88 1 .900 0.2770 30.3 0.2448 9/0.0322 279.5 16.72 + A variation of i 0.01 degrees in 29 causes a variation of 0.02A in the length of cn Substitution of the value of cQ in equation (4) yields the following: 0.0272 Nh + 0.0036 l2 (?) By substitution of the permissable values of and 1 in equation (5) a list of possible planes and their spacings was obtained (Table 26, pages 60, 61). The hinsdalite pattern was then indexed by comparison with these data. Calculation of indices and cell constants for the actual rhombohedral cell of this mineral was made by use of the following relat ionships : 1. Transformation to Rhombohedral Indices Rhomb. Hex. h = l(2h + k + 1) k = ■j( -h + k + 1) 1 = ■k-h - 2k + 1) Calculation of Rhombohedral------Cell Edge -- a.Q Rhomb. Hex. = 2 arh 3 J3ao2 + c 0 Calculation of Rhombohedral Cell angle a Rhomb. Hex. _3, ... 1 sin ^ = ) 2 /3 + (f)2 Calculation of Cell Volume. Rhomb. Hex. 3Vrh = Vhex = RaRcp 2 • 59* These relationships gave an a ^ value of 6.88A, an a value of 6l°8f and a volume of 236*?1AJ for the rhombohedral cell. The specific gravity of hinsdalite was calculated by use of the chemical data given by Larsen and Schaller (Op.Cit. p. 254) and the unit cell volume. The equation for the specific gravity can be written: 24 r _ M.1CT^ ^ N.V Where "M” is the molecular weight, "N" is Avagadros' Number and "V" is the volume of the unit cell. Palache et al (Op. Cit. p. 1004) give the ratio of lead to strontium in Colorado hinsdalite as ^ : 1 although a more accurate value for the determination of specific gravity is 4.7 : 1 • This yields a value of 557*35 for the molecular weight of the mineral and specific gravity is given by: G _ 657.^5 x 102l+ 6.02 x 1023 x 236.51 = 3-91 The complete X-ray data for Colorado hinsdalite are given in Table 27 (pages 62, 63, 64). • 60 • TABLE 26. Possible Indices and Interplanar Spacings for Hinsdalite. bk. 1 d hk.l d hk.l d hk.l d 41.9 5.698 10.1 11.9 1.640 04.8 1.227 14.9 1.078 30.6 05.1 1.210 00.3 5.573 03.6 1 *636 33.6 1.076 01.2 4.909 10.10 1.611 32.7 1.202 04.11 1.072 11.0 3.500 13.4 1.560 50.2 1.200 32.10 1.070 41.6 10.4 3.440 12.8 11.15 1.544 14.6 1.195 1.063 02.1 2.983 40.1 1.510 13.10 1.186 12.14 1.060 11-3 2.975 31-5 1-503 02.13 1.181 51.4 1.054 01.5 2.927 04.2 1.492 01.14 1.173 50.8 1 .049 20.2 2.850 22.6 1.482 33.0 1.167 15.5 1.036 00.6 2.785 01.11 1.470 05-4 1.165 24.7 1.033 02.4 2.454 02.10 1.464 23-8' 1.158 10.16 1.031 21.1 2.270 40; 4 1.425 30.12 1.144 03.12 23.11 1.025 20.5 2.246 00.12 1.389 24.1 1.143 13.13 1 .020 60.0 32.1 1.386 1.142 10.7 2.223 33.3 06.0 1 .010 11.6 2.180 04.5 1.380 50.5 1.140 42.8 1.005 30.0 60.3 2.021 13-7 1-375 42.2 1-135 0.9944 03-0 06.3 21.4 2.009 23.2 1.372 31.11 1.126 51-7 0.9909 01.8 1-975 30.9 1-367 40.10 02.16 0.9887 03-9 1.123 61 TABLE 26. Possible Indices and Interplanar Spacings For Hinsdalite Cont *d. hk.l d hk.l d hk.l d hk.l d 30.3 1 .900 20.11 1-356 O.988O 03-3 21.13 1.119 33-9 12.5 1.890 21.10 1 *350 00.15 1.115 05.10 0.9815 41.0 1.876 20.14 40.13 02.7 14.0 1-323 1.113 0.9789 00.9 1.857 32.4 1.320 24.4 1.105 03-15 0.9766 30.15 22.0 1-750 41.3 1.287 22.12 1.088 31.14 14-3 0.9743 20.6 1.720 23-5 1.284 51-1 1.087 01.17 0.9721 13.1 1-673 40.7 1.280 42.5 1.084 21.16 0.9493 22.3 1.670 22.9 1.274 30.13 1.083 21.7 1-653 12.11 1.264 05.7 1.082 31-2 1.64-9 10.13 1.254 1 5-2 1.080 62 TABLE 27. X-Ray Data for Colorado Hinsdalite. Hexagonal Rhombohedral .00 i o.ou = 6.88 ± 0.02A ao - 7 aiH a = 61°8' i 10 1 °0 = 16.72 t 0.05A c/a = 2 .39 t 0.01 V = 236.51 A3 G = 3-92 d Hex. Rhomb. d calc. 2© 1/11 hk.l hkl Hex. 15-55 5-7 0 92 10.1 100 5.698 15.90 5-57 30 00.3 111 5.573 18.10 4.90 3 01.2 110 4.909 25-47+ 3.50 44 11.0 10T 3.500 25.85 3-45 18 10.4 211 3.440 30.15+ 2.964 100 11.3 210 2.964 30.50 2.93 4 01.5 221 2.927 31.40 2.848 11 20.2 200 2.850 32.12+ 2.787 15 00.6 222 2.785 36.65 2.452 10 02.4 220 2.454 39-70 2.269 8 21.1 20T 2.270 40.10 2.248 12 20.5 311 2.246 40.55 2.224 86 10.7 322 2.223 4o. 80 2.21 1 17 12.2 21 T 2.212 41.35 2.183 15 11.6 321 2.180 30.0 2T1 44.90 2.018 2 2.120 03.0 112 45.10 2.010 10 21.4 310 2.009 .63. 2© d l/l, Hex. Rhomb. d calc. hk.l hkl Hex. 45.85 1.978 9 01.8 332 1.975 4?.88+ 1.900 30.3 300 1.900 36 03.3 22T 49.05 1.857 1 00.9 333 1.857 52-30+ 1.750 16 22.0 202 1.750 53.15 1.722 8 20.8 422 1.720 55.05 1.668 4 22.3 31T 1.670 55.50 1.655 11 21 .7 421 1-653 55.95 1.642 29 1 1.9 432 1.640 57-00 1.614 8 10.10 433 1.611 61.75 1.502 4 31.5 410 1.503 62.25 1.491 4 04.2 222 1.492 62.70 1.480 22 22.6 420 1.482 63.4p 1.465 24 02.10 442 1.464 65.50 1.426 4 40.4 400 1.425 67-20 1.392 3 00.12 444 1.389 68.25 1-373 4 23.2 312 1.372 68.60 1-366 8 30.9 522 03:9 441 1-367 69-55 1.351 6 21.10 532 1-350 41.0 3T2 71.30 1.321 3 14.0 213 1.323 32.4 411 1.320 72.90 1.295 7 11.12 543 1.291 64 2© d i/q Hex. Rhomb. d calc. hk.l hkl Hex. 41.3 4oT 1.287 73-60 1.286 9 14.3 322 1.284 23-5 421 75-45 1.258 8 10.13 544 1.254 32.7 520 1.202 79-80 1.200 9 50.2 4TT 1.200 X • OO o ---- 1.185 8 02.13 553 1.181 82.05 1.173 3 01.14 554 1-173 30.12 533 1.144 84.30 1.147 1 03.12 552 24.1 3U 1.143 84.90 1.14-1 2 33-3 412 1.142 50.5 500 1.14o 40.10 622 1-123 86.70b 1.121 6 21.13 643 1.119 92.85 1.064 3 11.15 654 1.063 4 24.7 53T 1-033 96.55 1-033 10.16 655 1.031 97-85 1.021 2 13-13 652 1 .020 60.0 422 99-55 1.010 1 06.0 224 1 .010 100.25 1.003 1 42.8 620 1.005 664 0.989 102.30 0.989 02.16 7 33-9 630 0.988 105.00 0.972 4 01.17 665 0.972 108.55 0.950 3 21.16 754 0.949 + 2© values determined by fixed count technique. 2. X-Rav Diffraction Studies of Beudantite Group Compounds* Time would not allow as an intensive a study of the Dundas pseudomorph and the synthetics, as of the Colorado hinsdalite. The scanning arc was limited to a maximum angle of approximately 60 degrees and the 29 values used to compute the cell constants were not checked by fixed count proced ures. The scanning rate and rate meter setting were the same as used for the hinsdalite. The calculations set out above were repeated for each set of results which are given in the following Tables 28 - 3^* 66 TABLE 28. X-Rav Data for Dundas Pseudomoroh. Hexasonal Rhombohedral a = 7*01 A arh = 6.90A 0 c = 16.74a a = 61 °8 1 0 c/a = 2.39 V = 238.04A3 G = 4.06 Hex. Rhomb. d calc. 29 d 1/11 hk.l hkl Hex. 15.55 5-7 0 94 10.1 100 5.698 15.90 5-57 17 00.3 111 5-573 18.05 4.91 17 01.2 110 4.909 25.40 3-51 59 11.0 10T 3.500 25.80 3-46 22 10.4 211 3.440 30.15 2.964 100 11.3 210 2.964 30.40 2.940 11 01.5 221 2.927 31.30 2.857 16 20.2 200 2.850 32.10 2.788 13 00.6 222 2.785 36.50 2.462 13 02.4 220 2.454 39-60 2.276 13 21.1 20T 2.270 40.05 2.250 13 20.5 311 2.246 40.50 2.226 32 10.7 322 2.223 40.70 2.216 27 12.2 211 2.212 41.30 2.186 13 11.6 321 2.180 45.00 2.014 10 21.4 310 2.009 . 67- TABLE 28. X-Rav Data for Dundas Pseudomornh Cont'd. Hex. Rhomb. d calc. 2© d I/1, hk.l hkl Hex. 45.80 1.981 01.8 332 1.975 300 47.85 1 .901 22 30.3 1.900 03-3 221 48.95 1.861 4- 00.9 333 1.857 52.20 1.753 15 22.0 202 1.750 53.10a., 1.724 4 20.8 422 1.720 54-. 90 1.672 3 22.3 31T 1.670 55.4oai 1.657 5 21.7 421 1-653 55-90a, 1.643 6 11.9 432 1.640 57-00 1 • 616 4 10.10 433 1.611 61.60ai 1.504 4 31.5 410 1.503 62.20 1-493 2 04.2 222 1.492 CO CM 62.65 1.481 4 22.6 420 • 63.35a, 1.467 8 02.10 442 1.464 68 TABLE 29. X-Rav Data for PbAiU(PO^) (SO^) (OH)^. (Synthetic Hinsdalite.) Hexagonal Rhombohedral aQ = 7>00A ^ = 6.88A arl c = 16.74A a = 61°81 c/a = 2.39 V = 237.37A3 G = 4.07 Hex. Rhomb. d calc. 29 d ^1 hk.l hkl Hex. 15.60 5.68 83 10.1 100 5.698 15.90 5.57 36 00.3 111 5.573 18.10 4.90 22 01.2 110 4.909 25.45 3.50 50 11.0 10T 3.500 25.85 3-45 32 10.4 211 3.440 30.15 2-965 100 11.3 210 2.964 30.45 2.940 14 01.5 221 2.927 31-40 2.848 18 20.2 200 2.850 32.10 2.788 27 00.6 222 2.785 36.55 2.459 18 02.4 220 2.454 39-65 2.273 16 21.1 20T 2.270 40.05 2.250 20 20.5 311 2.246 4o.45 2.229 45 10.7 322 2.223 40.75 2.214 27 12.2 21 T 2.212 41.30 2.186 18 11.6 321 2.180 • 69 • TABLE_29.. X.Rav Data for PbAl. (FQ^ ) (SQ^ ) (OH) . . (Synthetic Kinsdalite.) Conttd. Hex. Rhomb. d calc. 2© d ^1 hk.l hkl Hex. 30.0 2TT 44.8o 2.022 2.120 9 03.0 112 45.05 2.012 14 21.4 310 2.009 45.75 1.983 11 01.8 332 1.975 300 47* 80ai 1 .901 30.3 1.900 29 03.3 22T 52.15ai 1-753 18 22.0 202 1.750 53-05 1.727 9 20.8 422 1.720 55* 4o 1 • 658 11 21.7 421 1-653 55.80 1.647 13 11.9 432 1.640 56.85 1.620 9 10.10 533 1.611 61.55 1.507 9 31-5 410 1.503 62.50 1.486 11 22.6 420 1.482 63.30 1.469 14 02.10 442 1.464 70 TABL2_J0. X-Rav Data for PbAl-RAsOlf) (SO^) (OH) (Synthetic Hidalgoite) Hexagonal Rhombohedral. a = 7.04A = 6.97A o arh 17.00A a = 60°43' co = c/a = 2.41 V = 243.82A3 G = 4.26 Hex. Rhomb. d calc. 20 d 1/11 hk.l hkl Hex. 15.50 5.73 65 10.1 100 5.735 15.75 5*63 23 00.3 111 5.634 17.95 4.94 10 01.2 110 4.945 25.35 3-52 65 11.0 10? 3-520 25-60 3-48 26 10.4 211 3.474 30.00 2.980 100 11.3 210 2.986 31.20 2.867 8 20.2 221 2.868 31.80 2.814 18 00.6 222 2.817 36.40 2.469 10 02.4 220 2.472 39.50 2.281 7 21.1 20T 2.284 39.85 2.262 9 20.5 311 2.264 4o. 20 2.243 7 10.7 322 2.245 40.60 2.222 28 12.2 21 T 2.224 41.30 2.186 13 11.6 321 2.181 44.80 2.021 10 21.4 310 2.023 30.3 300 47.75 1.904 29 1.912 03.3 221 • 71. TABLE 30. X-Rav Data for PbAl., (AsO^ ) (SQ^) (OH). . (Synthetic Hidalgoite) Cont*d. Hex. Rhomb. d calc. 29 d V11 hk.l hkl Hex. 48.40 1.880 4 00.9 333 1.872 51-90 1.761 18 22.0 202 1.760 54.50 1.683 6 22.3 31T 1.680 54.95a-, 1 • 669 7 21.7 421 1.667 55-40 1 • 658 9 11*9 432 1.657 56 • 45 1.630 4 10.10 433 1.629 • 00 61.10 1.517 2 40.1 3TT vn 63.00a-| 1.474 9 02.10 442 1.478 72 TABLE 31 . X-Rav Data for PbAl, (VO^ ) (S0V|) (OH),. Hexagonal Rhombohedral 7.05k = 7.00 ao = ar Tr 17.10A a = ° ' co = 60 20 c/a = 2.43 V = 245.96A^ G = 4.06 Hex. Rhomb. d calc. 20 d T/Il hk.l hkl. Hex. 15.45 5.74 44 10.1 100 5.750 17*90 4.96 19 01.2 110 4.973 20.85 4.26 v+ 23*30 3.82 V 24.55 3-63 V 25-60 3-48 V 26.70 3*3^ V 27*70 3*22 V 29-65 3*01 100 11*3 210 3*001 29*90 2*99 20 01.5 221 2*991 31.40 2.849 12 00.6 222 2.858 36.30 2.475 6 02.4 220 2.487 21.1 20T 2.288 39-50 2.281 19 20.5 311 2.281 40.30 2*237 31 11.6 321 2.220 41.70 2*166 V 43.75 2.070 V 73- TABLE . X-Rav Data for PbAl-.(VO',) (SOi,) (OH)^. Cont'd. Hex. Rhomb. d calc 29 d 1/11 hk.l hkl. Hex. 44.65 2.029 10 21.4 310 2.032 46.00 1-973 V 02.7 331 1.911 47-75 1.905 5 00.9 333 1.906 50.90 1.794 V 51.65 1.770 7 22.0 202 1.763 52.50 1.743 V 53-75 1.705 V + Spacings noted ‘ 'V" recorded from unaltered vanadinite. • 74. TABLE ^2. X-Rav Data for PbFe.CPO^)(SO^)(OH)^. (Synthetic Corkite) Hexagonal Rhombohedral 7.32A = 7.00A ao “ art a = 63°00 co 16.75A c/a = 2.29 V = 259.72A3 G = 4.27 Hex. Rhomb. d calc. 20 d 1/I1 hk.l hkl Hex. 14.90 5-95 80 10.1 100 5.944 24.30 3-66 35 11.0 10T 3-665 25.35 3-51 10 10.4 211 3-517 28.65 3-11 100 02.1 11T 3.120 29-10 3-070 20 11.3 210 3.073 31.85 2.810 20 00.6 222 2.817 35.40 2.536 20 02.4 220 2.538 37-90 2.373 10 21.1 20 T 2-376 39-05 2.307 15 20.5 311 2.314 40.05 2.250 4o 10.7 322 2.257 30.3 21T ^5.85 1.979 25 1.981 03-3 112 46 • 45 1.955 7 12.5 320 1-957 49.80 1.831 20 22.0 202 1-833 75 TABLE ^2. X-Rav Data for PbFe^(PO^) (SO^) (OH)/•. (Synthetic Corkite) Cont *(1. Hex. Rhomb. d calc. 29 d 1/11 hk.l hkl Hex. 52.10 1.756 20.8 422 1.759 53*95 1.699 15 21.7 421 1.702 54.65 1.679 3 11.9 432 1.672 60.35a-, 1*533 25 22.6 420 1-536 62 • 4oa.j 1.487 30 4o. 4 400 1.486 TABLE 33. X-Rav Data for PbFe-, (AsOi, )(S0i|) (OH)^. (Synthetic Beudantlte) Hexagonal Rhombohedral 7-35A = 7.08A ao = arl co = 16-99A a = 62°36' c/a = 2.31 V = 265-61A3 G = 4.4? Hex. Rhomb. d calc 20 d 1/11 hk.l hkl Hex. 14.8? 5.97 58 10.1 100 5.960 15.70 5-65 5 00.3 111 5-659 24.20 3.68 34 11.0 10T 3-676 26 • 60 3-35 M+ 27.85 3-20 M 28.50 3-13 100 02.1 11T 3-128 29-10 3-070 14 11-3 210 3.081 29.95 2.980 M 31-60 2.830 12 00.6 222 2.829 35-25 2.546 20 02.4 220 2.547 37-7? 2.383 9 21.1 201* 2.381 38.90 2.315 9 20.5 311 2-319 39.85 2.262 18 10.7 322 2.266 30.3 21T 45.70 1.985 26 1.986 03-3 112 46-30 1.961 4 12.5 320 1.960 .77. TABLE X-Ray Data for PbFe.UsO^) (SO^) (OH)^. (Synthetic Beudantite) Cont!d. Hex. Rhomb. d calc. 29 d i/iv hk.l hkl Hex. 49.60 1.838 12 22.0 202 1.837 59.10 1.562 M 60.10 1.540 20 22.6 420 1.541 62.1 5 1.492 16 40.4 400 1.490 + Spacings noted "M" due to unalt ered Mimetite. .7 8. TABLE 34. X-Rav Data for PbFe,(VO)[) (SO^) (OH)^■ Hexagonal Rhombohedral = 7-12A a0 = 7-37A aid cQ = 17-12 A a = 62°24' c/a = 2-32 V = 269.08A3 G = 4.25 Hex. Rhomb. d calc. 20 d 1/11 hk.l hkl Hex. 14.80 5-99 70 10.1 100 5.987 20.60 4.31 v+ 24.10 3-69 55 11.0 10T 3.688 26.35 3-38 V 27-30 3.27 V 28.30 3.15 55 02.1 11T 3-141 29-80 3.09 100 11.3 210 3.080 29.80 3-00 V 31-35 2.853 4o 00.6 222 2.858 39-60 2-276 4o 10.7 322 2.287 41.20 2.191 V CO 0 • 2.161 V 43.85 2.065 V 44.70 2.027 V 46.00 1.973 V 48.40 1.881 V 79 TABLE 34. X-Rav Data For PbFe-.(V01|) (SO^) (OH). Cont'd. Hex. Rhomb. d calc. 2© d I/I1 hk.l hkl Hex. 1+9.40 1.845 40 22.0 202 1.845 55-80ai 1.646 • V 56.80a^ 1.620 V 61.40 1.510 15 02.10 442 1.511 + Spacings noted 1 'Vn due to unaltered vanadinite. .80. It is not proposed to consider the structure of the Beudantite Group in any detail as the subject has been well covered by previous workers. Henricks (Op.Cit.) studied the structure of the alunites and jarosites and from X-Ray data and the observation that alunite appeared to be pyroelectric referred them to space group R3m. Pabst (19^7) utilized the work of Henricks to establish the structure of the strontium (svanbergite) and calcium (woodhouseite) bearing members of the Beudantite Group. Pabst referred the minerals to space group R3m since the atoms can be considered to be centro- symmetrically disposed about the uni- or divalent cation and the pyroelectric properties of alunite have not been estab lished for certain. For the Beudantite Group minerals the space group could be R3m if the phosphorus and sulphur ions each occupy one of the positions on either side of the di valent cation rather than sharing both positions between them. Using the cell data for hinsdalite and the atomic structure elucidated for woodhouseite by Pabst (Op.Cit.p.22) an approximate scale projection of the atomic arrangement of the former mineral was prepared and is shown in Figure 5 (page 81). The cell data for the lead bearing members of the Beu dantite Group are given in Table 35 (page 83). The morpho logical value for the ratio of c : a and some crystallo- chemical data, relevant to the discussion of cell dimensions 81 Figure 1 Atomic Arrangement of Hinsdalite with Cel] Outline, an Aluminium and I hosphate Ion Shown in Heavy Print. .82. to follow, are also included in the table. The literature values of the morphological ratio have been doubled so that they conform with the structure of the group. The poor agreement between the ratios from X-ray and morphological studies is probably due to the lack of availability of well crystallized specimens for the latter studies. .83. TABLE ^5. X-Rav and Crvstaliochemical Data for Beudantite Group Minerals. Rhombohedral Hexagonal Morph. Mineral Specific Gravity Crystallochemical Data a V arh ao co c/a c/a calc. lit. Cation Radius Anion Bond Lengths* Hinsdalite Al^+ P-0 PbAl^PO^KSC^XOH^ 6.88 61°081 237.37 7.00 16.74 2.39 2.53 4.07 3*65 0.51 A 1.54A Hidalgoite As-0 PbAl:((As0lf)(S0lf)(0H)6 6.97 60°43' 243.82 7.04 17.00 2.41 4.26 3-96 1.75A V-0 PbAl^(VO^) (SO^) (OH)^ 7.00 60°20 1 245.96 7.05 17.10 2.43 4.06 1.76-1.95A Corkite Fe3+ PbFe^(PO^) (SO^) (OH)g 7.00 63°00' 259.72 7*32 16.75 2.29 2.37 4.27 4.295 o.64a Beudantite ■ PbFe^(AsO^)(SO^)(OH)^ 7.08 62°36 1 265.61 7.3? 16.99 2.31 mm 4.45 4-4.3 PbFe^(VO^)(SO^)(OH)^ 7.12 62°24' 269-08 7.37 17.12 2.32 - 4.25 - + No actual data is available for the anion bond lengths in the lead members of the Beudantite Group minerals. The work of Pabst (Op.Cit.) shows that there is little variation from the bond lengths in the simple ortho compounds and these values are given for the P-0 and As-0 bonds. Unfortunately the only values available for the V-0 bond are for bismuth vanadate (Qurashi, M.M. and Barnes, W.H. , 1953? Am* Mineral, 38, *+89.) which is a highly distorted structure. It is reasonable to expect, however, that the undistorted V-0 bond would lie somewhere within the extreme values given for the former vanadate. .84. The increase in the size of the unit cell with the sub stitution of ions of increasing radius is apparent from the increase in length of the rhombohedral cell edge of the min erals listed in Table From Figure 5 it can be seen that the trivalent cation is located halfway along the rhombo hedral cell edge* Comparing hinsdalite and corkite, for ex ample, the increase in ionic radius from 0.?1A for aluminium to 0.67A for iron results in an increase in the length of the rhombohedral cell edge, a ^ from 6*88A to 7*00A. The sub stitution is also accompanied by an increase in the rhombo hedral cell angle, a, and this accentuates the increase in the hexagonal aQ dimension whilst the cQ dimension remains virtually unaltered. The trivalent anion is situated on the three fold axis and in this position, changes in its size have a marked effect on c . Because of their high polariz ability the "ionic radii" of the anions vary widely accord ing to the structural environment in which they occur and no figures can be given. The approximate lengths of the bonds between the oxygen ions and the phosphorus, arsenic and van adium ions of the anion complex, however, enable an explan ation of the effect of these anions on the cell dimensions. The arrangement of the trivalent anion is such that the pent- avalent ion lies on the three fold axis directly above or below one of the tetrahedrally directed oxygen ions. An in crease in the length of the bond between this pair of atoms is reflected in the increase in the cQ dimension of hinsdalite, .8?. hidalgoite and their vanadium analogue, for example. Fur ther reference to Figure 5 shows that the increase in the length of arh must also be largely due to the increase in the length of this particular bond. The other three oxygen ions are so arranged that increases in the lengths of the bonds to the pentavalent ion occur almost normally to the directions of the rhombohedral cell edges and thus have min imal effect on their length. On the other hand, the small increment in the length of aQ is to be attributed to the in creasing length of the three Mrhombohedrallyu directed oxy gen ions since the remaining bond is directed normally to aQ The specific gravity determinations for hinsdalite and hidalgoite vary widely from those determined by physical means. From general considerations it can be shown that the value given by Larsen and Schaller (Op.Cit. 'p. 252) for hins dalite is too low. The Colorado mineral contains strontium, as well as lead in the ratio 1 : 4*7 and hence its specific gravity can be calculated by considering it to be a mixture of the two pure minerals svanbergite (G = 3*24) and hinsdal ite (G = 4.07) in the proportions stated. This approach yields a value of 3*98 which is compatible with the value calculated for the mineral (3»92). The deviation of the value for hidalgoite has been stated by Smith et al (Op.Cit. p. 1221) to be due to the presence of impurities in the sam ple used for physical measurement and this is probably also .86. the case with hinsdalite. The value obtained for synthetic hidalgoite (4.26) is in agreement with that calculated for the natural material (4.27)» 3. X-ray Diffraction Studies of Plumbogummite Group Minerals. The procedures were repeated for the synthetic plumbo gummite and its iron analogue and the results are given in Tables 38 and 37 (pages 87, 88, 89)* The effect of the tri- valent cation upon the cell dimensions is again noticable in these compounds. .87. TABLE 36. X-Rav Data for PbAl. (PO^) „( OH)H„0. (Synthetic Plumbogummlte.) Hexagonal Rhombohedral a = 7-01A = 6.90A 0 arl c0 = 16•74A a = 61°8' c/a = 2-39 V = 238.04a3 G = 4.06 Hex. Rhomb. d calc. 2© d hk.l hkl Hex. 15-50 5-72 20 10.1 100 5-716 15-85 5-59 10 00.3 111 5. 580 18.00 4.93 5 01.2 110 4-932 25-35 3-51 10 1 1 .0 10T 3.508 25-75 3-46 6 10.4 211 3.468 30.00 2.98 100 11.3 210 2.978 31-25 2.862 20 20.2 200 2.858 32.00 2.796 6 00.6 222 2.790 36-45 2.465 4 02.4 220 2.466 39-55 2.278 3 21.1 20T 2.275 39-95 2.256 4 20.5 311 2.259 40.40 2.232 10 10.7 322 2.226 40.65 2.219 5 12.2 211 2.216 Vi .15 2.194 6 11.6 321 2.196 44.90 2.018 2 21.4 310 2.017 88. TABLE ^6. X-Rav Data for PbAl~RPQ^) ^( OH)H^Q (Synthetic Plumbogummite) Cont'd. Hex. Rhomb. d calc. 29 d 1/11 hk.l hkl Hex. 45-75 1.983 15 01.8 332 1.990 30.3 300 47-75 1.905 10 1.906 03-3 22T 52.05 1.757 2 22.0 202 1.754 54.75 1.676 2 22.3 31T 1.674 55-30 1.661 1 21.7 421 1.664 55-75 1.649 1 11.9 432 1 • 656 62.35 1.489 1 22.6 420 1.489 63-20 1.471 3 02.10 442 1.477 .89. TABLE T7. X-Ray Data for PbFe-,(PO^ )VOH) ^.H„0. Hexasonal. Rhombohedral. = 7.04a aQ = 702 A arl1 cQ = 16.88A a = 62°361 c/a = 2.31 V = 261.74A3 G = 4.24 Hex. Rhomb. d calc. 2© d V11 hk.l hkl Hex. 14.90 5.95 30 10.1 100 5.934 24.25 3-67 10 11.0 10T 3.660 25.25 3-53 3 10.4 211 3-516 28.55 3.12 100 02.1 11T 3-114 29.10 3.07 15 11.3 210 3-069 31.80 2.813 10 00.6 222 2.817 3500 2. 542 5 02.4 220 2.535 37.90 2.373 7 21.1 20T 2.370 39.00 2.310 4 20.5 311 2.312 39.95 2.256 5 10.7 322 2.256 49.75 1.832 5 22.0 202 1.829 52.05 1-757 3 20.8 422 1-758 53-90 1.701 2 21.7 421 1.701 55-05 1.668 1 11.9 432 1.671 60.30 1-535 2 22.6 420 1.534 • 90. 4. X-Rav Diffraction Study of Plumbo.iarosite. It was found in the mineral synthesis section that the secondary lead minerals showed no tendancy towards alteration to compounds whose structure was similar to plumbojarosite. Hence no synthetic equivalent of this mineral was available for X-ray study. Since there is no indexed list of spac- ings on record for this mineral, a specimen (from the Tintic Standard Mine, Dividend, Utah, U.S.A.) was obtained from the Australian Museum, for study. The X-ray procedure and cal culations were the same as in the above investigations and the resulting data are given in Table 38? pages ^ , 92* The cell dimensions obtained from this study agree with those calculated by Henricks (Op.Cit. p. 778) from single crystal data for plumbojarosite from the original locality at Cooks Peak, New Mexico. • 91 • TABLE 38. X-Ray Data for Plumbo.iarosite. Hexasonal Rhombohedral a = 7.20A 0 arh = 11'94A c = 33.60A a = 35°001 0 o/a = »f. 6 7 V = 504.05A3 G = 3.72 Hex. Rhomb. d calc. 29 d 1/11 hk.l hkl Hex. 7.90 11.18 72 00.3 111 11.179 1 if. 4o 6.15 5 10.1 100 6.130 15.15 5* 86 01.2 110 844 15-85 5-59 9 00.6 222 5.587 17-65 5.02 5 10.4 211 5.000 19.45 4.57 7 01.5 221 4. 554 23.30 3.82 9 10.7 322 3.800 23.85 3.73 36 00.9 333 3-726 24.60 3.62 9 11.0 10T 3.6OO 25.60 3-^8 5 01.8 332 3.478 29.10 3.07 27 02.1 110 3-075 30.20 2.96 5 10.10 433 2.953 31-85 2.808 100 20.5 311 2.802 32.70 2-740 6 01.11 443 2.738 3^.65 2.590 14 11.9 432 2. 588 37-65 2.392 5 10.13 544 2-383 39.30 2.293 5 21.1 20T 2.289 • 92. TABLE 38. X-Rav Data for Plumbo.iarosite. Cont'd. Hex. Rhomb. d calc. 29 d IA1 hk.l hkl Hex. 12.2 21 T 2.273 40.50 2.275 45 02.10 442 2.271 45-90ai 1.975 11 02.13 553 1.979 46.45ai 1*953 3 03.6 330 1.948 48* 05a-j 1.892 11 21.10 532 1.893 49.55a., 1.838 5 12.11 542 1*833 51*455-1 1.774 4 22.3 31? 1-777 53*95a-| 1*697 4 13*4 32T 1.694 55*05ai 1 • 666 3 03-12 552 1.668 3?T 4 40.1 1.557 59.45a-, 1*554- 04.2 222 1.552 62.35a-, 1.488 20 40.7 511 1.482 66.30a-] 1.408 5 32.4 4lT 1.410 66.75a-] 1.400 6 23*5 421 1-399 69 *6 5a-] 1.348 3 41-3 4oT 1.351 76.60a-] 1.243 5 50.2 4TT 1.244 •93- 9. Chemical Spot Testing of the Dundas Pseudomorph. Since the X-ray diffraction results for plumbogummite and hinsdalite were very similar, this means of investigation did not allow the identification of the Dundas pseudomorph. The amount of material available was not sufficient to allow quantitative analysis and hence chemical spot testing was applied to the problem. The distinction between plumbo gummite and hinsdalite on the basis of spot testing inform ation is the presence of sulphate in only the latter of these minerals. The fading of a barium rhodizonate spot by the action of a solution containing sulphate was used as the test and this was found to be positive for the Dundas pseudomorph. This information indicates that the mineral is possibly hins dalite. This test was not considered conclusive however as the possibility of presence of sulphate from traces of an other mineral (anglesite for example) could have caused the positive reaction. 6. Differential Thermal Analysis. The presence of water in minerals of the Plumbogummite Group and it absence from those of the Beudantite Group sugg ested that Differential Thermal Analysis might be of use in distinguishing between them. An examination by this means was made of the synthetic equivalents of hinsdalite, corkite, plumbogummite and its iron analogue, Colorado hinsdalite and the Dundas pseudomorph. The results are shown in Figure 6 (page 95) and these reveal an endothermic peak at 120°C, corresponding to water loss, in only the Plumbogummite Group synthetics. The absence of this peak from the record for the Dundas pseudomorph confirms the indication from the spot testing that the mineral is hinsdalite. • 95* PbAl,(PO.)(SO.)(OH PhAl Hinsdalite, Colorado Hinsdalite, Dundae Temperature C. Figure 6. Differential Thermal Analysis Curves for Beudaritite and Plumbogummite Group Compounds. PART IV CONCLUDING REMARKS. 1. Some Reflections on the Dundas Pseudomorph. The identification of the Dundas pseudomorph as hins- dalite raises the problem of the origin of this mineral in the Dundas environment. The occurrence appears to be the first record of hinsdalite from the oxidized zone, the orig inal location being in a hydrothermal vein. Likewise, hid- algoite has only been reported from a hydrothermal associat ion although beudantite and corkite are typically oxidized zone minerals. In either environment, an abundance of aluminium is the unusual requirement which probably explains the rarity of the mineral. During differentiation of a magma the bulk of the aluminium is incorporated in the rock forming minerals. Un less the parent magma was unusually rich in this constituent, or upon cooling it followed a peculiar differentiation path, it is unlikely that aluminium would appear as a component of the hydrothermal solution. In the weathering process alum inium has low mobility and it tends to remain bound in the clay minerals. Unfortunately, little is known of the Dundas mineraliz ation since the mines of the area ceased operations before detailed geological investigations were undertaken. The gen eral environment is one of a mineralized contact zone, .97. between ultra-basic rocks and eugeosynclinal sediments and volcanics. The abundance of aluminium in the environment is clearly shown by the presence of a considerable quantity of gibbsite, A1(0H)^, which is closely associated with the oxid ized zone minerals of the area. The origin of the aluminium is not known, but if a hydrothermal source is discounted then there remains only the Dundas sediments. These sediments are represented by the typically eugeosynclinal rock types with greywackes, tuffs and shales making up a considerable portion of the stratigraphic section. Whilst no analyses are avail able for this association it is likely that it would contain more than average amounts of aluminium. Redistribution of the metal following hydrothermal alteration of the sediments could explain its presence in the environment. On the other hand it might also become available during erosion of the sediments if the conditions were such as to either prevent the formation of clay minerals or accelerate their subsequent destruction. The soil waters of western Tasmania have pH values as low as 3.5 and are relatively rich in humic acids. Such waters have a strongly corrosive action on the rocks with which they make contact and could well be the means by which aluminium is released from its normal silicate hosts. A further point of interest is that Petterd (1910) in a study of the minerals of Tasmania recorded the presence of plumbogummite on a specimen of partially decomposed galena from Zeehan. A small piece of this material was found to be still available in the Petterd Collection of the Tasmanian Museum and this institution kindly loaned it for examination. Under the binocular microscope an off-white resinous mineral associated with other unidentifiable minerals was seen to be developing as an alteration product of a fine crust of pyro- morphite which coated the galena. The material did not allow a check of the original determination but the test for sulphate was positive. As hinsdalite was unknown at the time of Petterd's study his specimen may in fact be this mineral. It is apparent from the mineral syntheses results, that both hinsdalite and plumbogummite are formed quite readily from pyromorphite. The pseudomorphing of pyromorphite by either of the minerals involves almost a quadrupling of the number of ions present in a given volume and as a result con siderable ionic movement must take place. One factor which probably influences the identity of the pseudomorph is the time at which aluminium enters the environment. If oxid ation of the ore body was actively proceeding at the time of arrival of the aluminium then the abundance of sulphate in the environment would enable this ion to compete with phos phate for available sites in the mineral lattice and hins dalite would result. If, on the other hand, the oxidation of the ore body was virtually complete by the time the alum inium arrived, sulphate would be at a far lower concentration • 99* and, provided that phosphate remained abundant, the formation of plumbogummite would take place. 2. Classification of the Alunite. Plumbogummite and Beudantite Groups. Many attempts have been made at the classification of these minerals and it was not until the advent of X-ray crys tallography that any real progress was made. As early as 1900, Prior (Op.Cit.) recognised that similarities in the composition of several complex phosphates indicated that they belonged to a natural mineral group. Amongst others, were listed plumbogummite 2PbO.3AlpO^.2Pb20^.7HpO and beu dantite 2PbO. IFe^O^.P^Oj--. 2S0^.6H90. In an attempt to accen tuate the close relationships between the minerals, Prior (Op. Cit. p. 251) recast the formula of beudantite as PbSO^.FePO^. Fep(OH)^ and to negotiate the difficulty caused by the appear ance of additional phosphate in plumbogummite a hydrogen phosphate grouping was considered to replace the sulphate so that the formula became PbHPO^.AlPO^.Alp(OH)^. In a study of the alunites and jarosites, Hillebrand and Penfield (Op. Cit. p. 218) gave a formula for plumbojarosite as Pb [FetOH^J^ [S0lf]4 although as an alternative they gave PbFe^(OH)^^(SO^)4. The latter formula is accepted today, although the practice is to reverse the places of the hydroxyl and sulphate ions. It is unfortunate that Schaller (Op.Cit. p. 364) chose the .100. first type of formula rather than the second given by Hiller- brand and Penfield on which to base a comprehensive classif ication of the minerals known at the time. Had he considered the chemical data in the light of the second formula there is little doubt that his classification would have been more or less consistent with that resulting from the results of later crystallochemical investigations. Schaller however hased his work on the first type of formula and used procedures similar to those of Prior to negotiate the problems of the minerals containing phosphate. He divided the minerals into sulphates, phosphates and sulphate-phosphates and proposed the general formula £r1 11 (OH)^]^ H11 [m]2 M 2 ’ ^ormula plumbojarosite thus being written [_Fe(0H)2]^ Pb[so^]^ For the phosphates and sulphate-phosphates the formulae con tain some peculiar groupings of ions and plumbogummite is written [ai(0H)2J^ Pb[HPO^J^PbCPO^)whilst beudantite be- comes [Fe(OH) 2 ]6Pb [S04]2[Pb(As0^)2 ]. The classification remained in the form proposed by Schaller until the advances in X-ray techniques enabled structural studies to be undertaken. Henricks (Op.Cit.) made a structural determination of the alunites and jarosites and recognised that the basic structural unit of these min erals was rhombohedral and that the cell contents could be expressed by the general formula R R -j (S0If)2(0H)^, alunite, for example, being K Al^(S0^)p(0H)^. Henricks also correctly 101 anticipated that the phosphates and sulphate-phosphates would have similar structures and formulas equivalent to that given for the sulphates. Plumbojarosite alone deviates slightly although its structure is almost the same as for the other minerals of the group. The presence of the divalent lead associated with a sulphate mineral requires a doubling of the remaining ions to achieve electrical neutrality. The formula thus becomes PbFe^(S01+)1+(0H)^ p and structurally this is brought about by the replacement of half the potassium ions of the alunite structure with lead ions whilst the remaining potassium sites are left vacant. The rigid chemical classification adopted by Palache et al (Op.Cit.) which is based on the identity of the predomin ant anion, raises the subdivisions of Schaller (Op.Cit.) to group status. The sulphates become the Alunite Group, the Phosphates, the Plumbogummite Group and the Sulphate-phosphates the Beudantite Group. In view of the very close structural and chemical relationships between the minerals their separ ation into the three groups does not appear entirely justif ied. The sulphate-phosphates may be considered to represent the mean between the sulphates at one extreme and the phos phates at the other. Consider, for example, alunite, hinsdal- ite and plumbogummite. Alunite K Al^ (SO^ (0H)6 Hinsdalite Pb Al^ (P0If)(S0l+) (0H)6 Plumbogummite Pb a13 (p parts from this value the composition moves towards either alunite or plumbogummite. With increase in sulphate content the total positive charge of the cations becomes excessive and this is counteracted by the substitution of a univalent ion (potassium) for the divalent lead. On the other hand, as the phosphate content is increased there is an excess of negative charge to be balanced and this is achieved by the substitution of neutral water for univalent hydroxyl. The presence of silver in the Dundas hinsdalite may represent some such balance for a slight excess of sulphate over the 1 : 1 ratio. The incorporation of silver into the alunite structure is known for one of the minerals, namely argentoj arosite , AgFe^( SO^^COH)^. The present study was aimed largely at the alteration of pyromorphite and related minerals to members of the Beudant- ite Group and direct mineral syntheses were not seriously undertaken. In the course of the experimental work however a number of the minerals were in fact produced from systems containing their constituent ions. No attempts were made to produce compounds intermediate in composition between the species of the three groups now recognised, but their close structural relationships suggest that little difficulty would be experienced in such syntheses. In the change from Beudant- ite Group minerals to those of the Plumbogummite Group, for .103. example, one hydroxyl ion in six is replaced by a water mol ecule to balance the gain in negative charge produced by the substitution of phosphate for sulphate. For an intermediate compound some sulphate would remain in the lattice and the proportion of hydroxyl ions replaced by water molecules would be correspondingly less than one in six. The strong relationships between the minerals suggested to the writer that a general formula could be devised and this takes the form: M1,.. y1 M111 (PCX ) (SCV) (OH). , -.H 0, . (1-y) y 3 H X 4 (2-x) 6-(x-y) 2 (x-y) For the Beudantite Group x = 1, y = 1, for the Plumbogummite Group x = 2, y = 1 and for the Alunite Group x = 0, y = 0. These figures yield the formulae 1 ^(PO^) (SO^) (OH)^ , M111 ^(PO^) 9(0H) H^O and 1 ^(SO^^COH)^ respectively for the three groups. The minerals considered in the present study are not common. Their separation into three distinct groups by strict anion classification, however, illustrates a weakness of this type of classification. If crystallographic and geo chemical behaviour of the anions were considered rather than chemical identity alone the minerals containing sulphate, phosphate and structurally related ions would not be separ ated. The Alunite, Plumbogummite and Beudantite Groups of minerals would all fall within one group and further subdiv ision could be made along the lines used by Schaller (Op.Cit.) into sulphates, phosphates and sulphate-phosphates. .104. APPENDIX ANALYTICAL PROCEDURES AND DETAILED RESULTS. 1. Determination of Lead. Lead analyses were made polarographically 9. using a Tinsley Recording Polarograph. Standards were made up to contain 0.01 - 0.02 mgs. Pb/ml. 10 ml. samples of standards and unknowns alike were pipetted into small beakers and 1 .0 gm. of potassium nitrate and 0*3 mis. of a 0aqueous starch solution were added to each. The samples were gassed in turn with nitrogen and run through the polarograph to record the lead wave which developed in the range 0.40 - 0.65 volts (vs.s.c.e). The wave heights of the standards are recorded in Figure 7 (page 105), which also carries the curve for lead. The analytical results for the determination of lead in the hinsdalite, corkite and pyromorphite reactant solutions are given in Table 39 (pages 106, 107)• 9. Kolthoff and Lingane (1952) p. 528. Lead Figure 7 Height Wave » Lead "ave Calibration Height 105 (cm.) Curve 106. TABL3 3Q. Analytical Results for Lead in Reactant Solutions. Wave Height mgs. Pb mgs. Pb Solution (cm*) in aliquot in sample 0 V co — O C\J 0 / • • CO Hinsdalite 1 A 0.83 0 0 B 0.86 0.221 1.110 C 0.86 0.221 1.110 2 A 1.18 0.303 1.515 B 1.13 0.295 1.475 C 1.16 0.302 1.510 3 A 1.19 O.308 1.540 B 1.21 0.312 1.560 C 1.20 0.310 1-550 4 A 1-25 0.324 1.620 B 1.24 0.322 1.610 C 1.22 0.314 1-570 Corkite 1 A 0. 56 0.145^10^ 0.725(t’°) B 0.58 0.147 0-735 C 0.61 0.158 0.790 2 A 0.51 0.132 0.660 B 0.48 0.126 0.630 C 0.51 0.132 0.660 3 A 0.41 0.107 0-535 B 0.45 0.114 0.570 .107. TABLE ^9. Analytical Results for Lead in Reactant Solutions Cont'd. Wave Height mgs. Pb mgs. Pb Solution (cm.) in aliquot in sample Corkite 3 0 0.42 0.109 0.545 4 A 0-35 0.090 0.450 B 0-35 0.090 0.450 C 0-35 0.090 0.450 Pyromorphite 1 A 6.90 1.860(10') 36.2(200) B 6 • 60 1.730 34.6 G 6.65 1.745 34.9 2 A 5-70 1.480 29-6 B 5.80 1.510 30.2 C 5.50 1.420 28.4 3 A 5.05 1.320 26.5 B 4.95 1.290 25*8 C 5.00 1.300 26.0 4 A 4.50 1.175 23.5 B 4.40 1.1 50 24.1 C 4.30 1.130 22.6 .108. 2. Determination of Aluminium. Aluminium was determined colorimetricly by extracting the metal as the yellow aluminium hydroxyquinolate * into chloroform. Standards were made up to contain 0.025 - 0.100 mgs. Al/ml. The standards and unknowns were diluted to 25 mis. and 1 ml. of 2.5^ sodium acetate was added to each. The pH was adjusted to 4.5 - 6*5 with 1$ ammonium hydroxide and 10 mis. of a J\% solution of 8-hydroxyquinoline was added. The samples were shaken for three minutes, the organic layer drawn off and dried by shaking with anhydrous sodium sul phate, and the absorbance measured at 395 mq in a Unicam SP500 Spectrophotometer. The results for the standards and the calibration curve are given in Figure 8, (page 110) whilst the results for the aluminium solutions are set out in Table 40 (page 109)* 10. Sandell (1959) P« 231. 109- TABLE 40. Analytical Results for Aluminium in Reactant Solutions* mgs. A1 mgs. A1 Solution Absorbance in aliquot in sample 1 A 1.760 0.072^°*2^ 18.12(50) B 1.720 0.0710 17.75 C 1-735 0.0715 17.87 2 A 1.280 0.0535 13-38 B 1.200 0.0^90 12.25 C 1.180 0.0485 12.13 3 A 0.810 0.0335 8.38 B 0.750 0.0310 7-75 C 0.800 0.0330 8.25 4 A 0.250 0.0100 2.50 B 0.270 0.0115 2.85 C 0.270 0.0115 2.85 110. C. 100 Absorbance 1.220 0.10C 1.0 Absorbance Aluminium Calibration Curve. Determination of Iron. The analyses of iron were made colorimetricly using a blue complex of iron with catechol. This appears to be a new method for trace iron and it was developed during study of the effect of iron on the determination of molybdenum with catechol *. The catechol reagent was made up by dis solving 15 gms. of sodium metabisulphite in 1000 mis. of 0.2% sodium hydroxide and then adding 10 gms. of catechol. Standards were made up to contain 0.1 - 1.0 mg. Fe/ml. The standards and unknowns were diluted to 10 mis. and a few drops of 1% sodium hydroxide were added to adjust the pH to 7*0. This caused precipitation of the iron but the precip itate redissolved on the addition of 10 mis. of catechol re agent to yield an intense blue solution. Spectrophotometric studies of the complex (in the 0.4 mg/ml standard) were undertaken to locate the wavelength at which the absorption was at a maximum. The graph of wave length versus absorption is given in Figure 9 (page 112) and it is seen that the maximum occurs at 570 mp. Measurement of the standards and unknowns was made at this wavelength. The calibration curve is given in Figure 10 (page 113) and the analytical results in Table 41 (page 114). 11. Seifter, S and Novic, B. (1951)? Colorimetric Det ermination of Molybdate with Catechol: Anal. Chem. 23, 188. Abaorbaric loir'll Wavelength re 540 500 4 520 440 400 460 420 BO o. Absorbance Absorbance O 0.779 0.680 0.670 0.722 1 1.061 1.173 Wavs .303 .922 length 112 Curve Complex. Wavelength cifi 700 800 625 620 600 58 560 550 for C Iron-Catechol Absorbance 0.124 0.568 1.125 1.171 1.275 1.342 1.315 1.352 113 Pb ni(< 1.041 Absorbance Figure 10. Iron 0alibration Curvo TABLE 41. Analytical Results for Iron in Reactant Solutions* mgs. Fe mgs. Fe Solution Absorbance in aliquot in sample 1 A 1.305 0.366(1) 18.30(^0) B 1.320 0.372 18.60 C 1.323 0.372 18.60 (1 ) 2 A 0.812 0.229 11.45 B 0.826 0.233 11.65 C 0.808 0.228 11.50 3 A 1.915 0.5*+3(?) 5.43 B 1.902 0.536 5.36 C 1.912 0.55-1 5.41 4 A 0.895 0.239^ 2.39 B 0.887 0.238 2.38 C 0.910 0.25-3 2.43 4. Determination of Phosphate. Phosphate was determined by the molybdophosphoric acid method *. Standards were made up in the range 0.025 - 0*500 mg P0^/ml. To 15 ml. volumes of the standards, 5 mis. of 12. Boltz (1958) p. 38. .11?. 1.25M nitric acid and 5 nils, of 10$ sodium molybdate were added. The absorbance of the resulting yellow colour was measured at 389 mp. 5 ml. samples of the hinsdalite and corkite solutions were taken and bulked to 1? mis. whilst 1? ml. samples were taken from the pyromorphite solutions. Each of these was determined in the same manner as for the standards. The phosphate calibration curve is given in Figure 11 (page 116), and the analytical results in Table 42 (page 117, 118). 116 Low Range \ 0.4 0.6 0 LI urr M. ho/ ■ •• o<; >: ' 10 ra*h sn Curv . 117 TABLE 42. Analytical Results for Phosphate in Reactant Solutions. mg P04 mg P04 Solution Absorbance in aliquot in sample Hinsdalite 1 A 1-735 0.431 ^ 4.31(?0) B 1-795 0.446 4.46 C 1.702 0.425 1-25 2 A 1.012 0.280 2.80 B 1.005 0.267 2.67 C 1 .010 0.278 2.78 3 A 0.632 0.160 1.60 B 0.695 0.173 1.73 C 0.653 0.162 1.62 4 A 0.299 0.076 0.76 B 0.221 0.058 0.58 C 0.260 0.072 0.72 Corkite 1 A 1.422 0.343(5) 3-43(?0) B 1-301 0.326 3-26 C 1-320 0.330 3.30 2 A 0.675 0.172 1.72 B 0.722 0.182 1.82 C 0.745 0.186 1.86 .118. TABLE 42. Analytical Results for Phosphate in Reactant Solutions Cont!d. mg P04 mg P04 Solution Absorbance in aliquot in sample Corkite 3 A 0.037 0.096 0.96 B 0.032 0.080 0.80 C 0.034 0.085 0.85 4 A 0.012 0.028 0.28 B 0.014 0.037 0.37 C 0.008 0.025 0.25 0.78(2°°) Pyromorph- 1 A 0.280 0.058^ ^ ite B 0.330 0.068 0.90 C 0.310 0.065 0.86 2 A 0.208 0.043 0.57 B 0.236 0.048 0.63 C 0.241 0.050 0.66 3 A 0.200 0.042 0.56 B 0.190 o.o4o 0.53 C 0.200 0.042 0.56 4 A 0.120 0.026 0.35 B 0.170 0.036 0.48 C 0.140 0.030 0.40 .119 9. Determination of Sulphate. Sulphate was determined turbidimetricly using solid 1 o barium sulphate crystals as the precipitant. Standards were made up in the range 0*5 - 2.0 mgs. SO^/ml. 10 ml. samples of the standards were mixed with 5 ml. of a salt- acid solution (240 gms. sodium chloride and 20 mis. of hy drochloric acid made up to 1000 ml. with water). 0.3 gms. of -25 + 35 mesh barium chloride crystals were added to each and the solution stirred for 1 minute before measuring the turbidity by means of an E.E.L. Nephelometer. 5 ml. samples of the hinsdalite and corkite reactant sol utions were diluted to 10 mis. and the above procedure re peated. The calibration curve is given in Figure 12 (page 120) and the analytical results in Table 43 (pages 121 and 122). 13- Sheen et al (1935)* 1 20 liephol crater Redinr Figure 1?» Sulphate Calibration Curve 121 . TABLE 4l. Analytical Results for Sulphate in Reactant Solutions. Nephelometer mgs. SO^ mgs. SO^, Solution Reading in aliquot in sample Hinsdalite 1 A 86 17.20(5°) B 78 1 • 56 1 5-60 C 80 1.60 16.00 It 2 A 60 1.20 12.00 B 62 1.24 12.40 C 58 1.16 11.60 3 A 44 0.88 8.80 B 4o 0.81 8.10 C 38 0.77 7*70 4 A 18 0-35 3-50 B 20 o.4i 4.10 C 20 0.41 4.10 Corkite 1 A 74 1.48 14.8 B 76 1-53 15.3 C 73 1.46 14.6 2 A 55 1.10 11.0 B 57 1*15 11.5 C 54 1.08 10.8 122. TABLE 43. Analytical Results for Sulphate in Reactant Solutions. Gont!d. Nephelometer mgs. SO^ mgs. S0k Solution Reading in aliquot in sample Corkite 3 A 32 0.65 6.5 B 27 0.55 5> 5 G 28 0.57 5-7 4 A 11 0.23 2.3 B 12 0.25 2.5 C 8 0.18 1.8 .123. 6. Determination of Chloride. Chloride was determined by titrating 20 ml. samples with 0.05N silver nitrate (1 ml. = 1.77 mg. Cl”) using fluorescein as an indicator. The analytical results are given in Table 44, below. TABLE 44. Analytical Results for Chloride in Reactant Solutions. Cl" mg. Cl” mg. Solution AgNO^ ml. in aliquot in sample v- C\J 0 0 C\j o 0 Pyromorphite 1 A 12.4 21.90(20) • B 12.2 21.60 216.0 C 12.9 22.80 228.0 2 A 9-6 17.00 170.0 B 9.4 16.65 166.? C 9-5 16.81 168.1 3 A 6.4 11.32 113.2 B 6. 5 11.50 115.0 C 6 • 6 11.69 116.9 4 A 4.0 7.09 70.9 B 3.0 5.31 53.1 C 3.5 6.20 62.0 ———.■■ ■ ...... — .124. REFERENCES BOLTZ, D.F. Ed., (1958), Colorimetric Determination of Non- metals. Interscience Publishers, Inc., New York. 372 pp. GARRELS, R.M. (i960), Mineral Equilibria. Harper and Bros., New York. 254 pp. GLASSTONE, S. (1951)5 Text Book of Physical Chemistry (2nd Ed.). Macmillan and Co. Ltd., London. 1320 pp. HENRICKS, S.B. (1937), The Crystal Structure of Alunite and the Jarosites: Am. Mineral, 22, 773* HILLEBRAND, W.F. and PENFIELD, S.L. (1902), Some Additions to the Alunite - Jarosite Group of Minerals: Am. Jour. Sci., 14, 211. HILLEBRAND, W.F. and WRIGHT, F.E. (1910), A New Occurrence of Plumbojarosite: Am. Jour. Sci., 30, 191 • KAUFFMAN, A.J. 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Publication. 221 pp. PRIOR, G.T. (1900), Hamlinite, Florencite, Plumbogummite (Hitchcockite), Beudantite and Svanbergite, as members of a natural group of minerals: Min. Mag., 12^ 249. SANDELL, E.B. (1959), Colorimetric Determination of Traces of Metals (3rd Ed.). Interscience Publishers Inc., New York. 1032 pp. SCHALLER, W.T. (1911) , The Alunite - Beudantite Group: Am. Jour. Sci., 32, 359* SCHEEN, R.T., KAHLER, H.L., ROSS, E.M. and BETZ, W.H. and L.D. (1935), Turbidimetric Determination of Sulfate in Water: Ind. and Eng. Chem. (Anal. Ed.) 7, 262. SMITH, R.L., SIMONS, F.S. and VLISIDIS, A.C. (1953), Hidalgoite, a New Mineral: Am. Mineral, 38, 1218.