M]NIJRALOGICAL NOTI'S 229

Talr,e 1. Cnrutcet Conpostrron ol Wnolvolrrtn lnon Vanrous Souncos

CaO 38 38 38.46 38 83 38.36 38 23 C:O: 49 28 49.65 49.38 50.28 48.69 HrO 12.34 72 74 123l 11.36 Not Determined

1. Ca(C:Oa).HrO 2. Pchery', Bohemia 3. Briix, Bohemia 4. Maikop, Caucasus 5. Milan, Ohio Note: Analyses 2,3 and 4 from Palache et ol. (195L).

This find is of interest for the following reasons: 1. It is the first reported in easternUnited States.2. It is the first of any sizablequantity in the United States.3. It is found in older rocks than previous finds. 4. The location is readilv accessibleto interested petrologists.

We are glad to acknowledgethe help of Mr. Owen Keim who per- formed the chemicalanalysis and Mr. C. R. Tipton, Jr. who made this work possibie,both of whom werethe authors' associatesat the BasicIn- corporated ResearchCenter. Of course,special thanks and recognition must go to Mr. ClarenceRaver rvhosupplied us with the samples.

RrlBnrNcos

Guon, A. J., 3rd, E. J. YouNc, V. C KnNNrov aNn L. B Rrr.r:v (1960) Wheu,ellite and celestitefrom a fault opening in San Juan County, IJtah- Am. .45,1257-1265. Per.ecun, C, H. BnnlreN aNo C FnoNou. (1951) Danos' SystemoJ Mineralogy, Vol. II, 7th ed., John lViley and Sons,Inc., Nelr' York. Pocon.r, W T eNo J. H. Krnn (1954) Whewellite from a septarian iimestone concretion in marine shalenear llavre, Montana Am. Mineral.Jg,208-214.

THE AMERICAN MINERALOGIST,VOL 51, JANUARY_FEBRUARY,1966

LACLTSTI{INE GLAUCONITIC FROM PI,UVIAL LAKE MOUND. LYNN AND'IERRY COUNTIES, TEXAS

W. T. Penny AND C. C. RBnvBs, Jr.., Texas Technological College,Lubboch, T exas.

Glauconitic mica from lacustrinesediments in pluvial Lake Mound, Ly-nn and Terry counties, Texas is identified by r-rav diffraction, optical 230 MINIiRALOGICAL NOTES measurements,differential thermal analysis and chemical anall'sis. Glauconiticmica occursin Lake Mound as pellets,streaks, or dissemina- tions in clastic and lacustrine dolomites with , and mixed la1'erclal's. There is no sourceof detrital glauconiteor glauconitic mica in the vicinitr'. The glauconitic mica is authigenic, formed by fixation of and potassiumin cla-r-mineral lattices in the lacustrine sediments. Glauconiteis an illite-t1'peclav mineral reported to form in marine waters(Cloud, 1955;Takahashi,1939) ;however, D1'dchenko and Kha- twtzeva (1956) find giauconitein alluvial and elluvial depositsof the Ukraine. Keller (1958) describesglauconitic mica in the Morrison Formation, Coloradowhich forms br'fixation of and iron in montmorillonite. Glauconiticmica, intermediatein compositionbetween glauconite and , contains more tetrahedral aluminum than glauconitebut lessthan muscovite.Glauconitic mica also containsmore octahedralaluminum and lessoctahedral ferric iron than glauconitebut lessoctahedral aluminum and more octahedralferric ion than muscovite. A silicatelattice, suppliesof potassiumand iron, and a favorableoxida- tion potential are necessaryfor the formation of glauconite(Burst, 1958) and glauconiticmica. Favorable oxidation potentials are producedin a marine environment b.v deca,vingorganic material, but silicatesma1'be altered to glauconite in the absenceof decafing organic matter in re- stricted basins,lagoons, or lakesin which semioxidizingconditions exist' 'Ierry-Lvnn Nlound Lake, located on the Count-vline 10 miles east of Brownfield, Texas, is one of a number of pluvial lake basins on the SouthernHigh Plains (Reeves,1962, 1963). Green , greenclal' and greenarenaceous clay have beenfound in 20 augerholes and pits beneath the presentplal'a. There are two persistentstratigraphic occurrences of the greensediments, a shallowzone with a depth rangeof 3] to 5 fee1.and a deeperzone ranging from 12 to 14 feet. The greensediments are alwaYs found near the present plal'a shore line and are commonly associated with gypsum cr.vstalsand gravels.Carbonate dates indicate that these sedimentspre-date the maximum \Visconsinadvance. Sampleswere collectedfrom both persistenthorizons. Samplesr'vere washedand dispersedin distilled water using calgon.Size separation was madeby sedimentationand orientedaggregates were prepared by vacuum fiitration on porousceramic plates for r-ray examination. X-ray diffractogramsof orientedaggregates (Fig. 1) are similar to dif- fractograms of weli-orderedglauconite (Burst, 1958). Weaver (1965) showsthe ratio of the (001)to (002)peak intensity is relatedto the potas- sium content in illite cla1.s.Mound Lake glauconiteshorvs an intensitr- ratio of 4 indicating57oKrO (Weaver,1965, Fig. 1) but chemicaianal1'sis MIN]].RALOGICALNOT]'S 231

(Table 1) reveals 3.80/6.X,ray diffractograms (Fig. 1) prove the ab- senceof expandablela1'ers and indicate that potassiumcontent is high enoughfor a stablemica structure. X-ra1. diffractogramsof random mounts (Fig. 2) do not show enough diffractionsto allow classificationof the glauconiteas a 1M structure but do suggestthe 1Md classificationeven though there are differencesfrom the 1Md glauconitesof Burst (1958).For example,the 3.05 A diffraction peak is missingfrom the Mound Lake material but is verv prominent in

UNTREATE D

GLYCEROL

550" c,

FrcunrI' x-rav mica ori en ted "i#:lff lltrf#t :'::iiil:"nitic the glauconitefrom the Burditt Formation, Texas, classifiedas 1Md by Burst. The prominent 3.32 A diffraction peak in the Mound Lake ma- terial is weak or missingin the Burditt glauconite. Glauconiticmica particle sizeis too small to obtain optical properties of singlefragments, therefore oriented aggregatesrvere examined. Glau- conitic mica pellets, oriented aggregates,and streaks are deep green in color and non-pieochroic.The deep green color is a result of high ferric iron content. Index of refractionmeasurements of orientedaggregates indicate only the averageof beta and gamma since alpha is nearly perpendicularto (001)and the a and 6-axesof individual fragmentsare randomly oriented 232 MINERALOGICAL NOTES

T,c.nrr 1. Ax,q.lvsrsor MouNo Larn Gr,.tucoNrrrcMrcL

Weight Per Cent

sio, 41.6 FezO; 16.1 l'eO o.7 Alzo: 11.0 Mgo 4.8 CaO 0.9 KzO 3.8 NorO J.J HzO (Releasedbelorv 115. C.) 38 HrO (Releasedbetrveen 115oC. and 1000"C.)

987

Semiquantitative Spectrographic Analysis

lilement (ppm/ Element (Ppm/

Mo r.) Ni 20 Sn 10 Ti 1200 V /JU Pb 65 Cu IJ Mn 85 Zn 35 Sr .tJ Ag 2 Cr 6.) Co I Ba 85 in the aggregate.The measuredindex of oriented aggregatesof Mound Lake glauconitic mica is 1.592+.005. This is low for glauconite with ferric content indicated in Table 1, but refractive indicesof glauconites

3.32 r.5l roa I I I

60 50 40 30 ?o to DEGREES2E COPPERK

Frc. 2. X-ray difiractogram of Mound Lake giauconitic mica. Random mount. Ni-filtered Cu radiation. MINP,RALOGICAL NOTL.S 233 are considerablvalfected by variable content of adsorbedwater in the crvstals(Sabatier', 1949, in Deer etal., 1962).Chemical analvsis (Table 1) shows12.?/6 water releasedbetween 115" C. and 1,000"C. and difieren- tial thermal anal1,siscurves of fine glauconiticmica (Fig. 3) show a pro- nounced endothermicpeak at 150' C. Both measurementsindicate ad- sorbedwater which accountsfor the low index of refraction. Results of chemicalanaiysis of the Mound Lake glauconiticmica are shorvnin Table 1. The calculatedformula excludingTiOz is:

+l 06 015 +++ ++ (CaoorNao:rKc ag)(Alo eqFeo ssFeo ouMgo uJ(Sir rsAloeJO'o(OH)z

Fro. 3. Differentt.tr;';;';1.".* 0",,*"s of MoundLake glauconitic mica. Equilibratedover saturated CaCl: solution, relative humidity 30%.

The material is clearly dioctahedralwith Fe3+as the principal octahedral cation. Foster (1956)indicates the compositionof the tetrahedrallay'er in giauconiteis (Si3.62A.16as)and that the rangein tetrahedralcomposition in muscoviteis (Si2.esto s rrAlr.ozto o.ss).The tetrahedrallayer of the Mound Lake material is intermediatebetween Foster'scomposition for glauco- nite and muscovite. Foster shows the octahedrallayer in muscovite is (AI1e6Fe6 i.rt* .) and the octahedrallayer in glauconiteis (Alo.rsFer.r3+ to rz .). The octahedrallayer in the Mound Lake materialis (Alo.u- Feoss8* . . . ) which is intermediate betweenmuscovite and glauconite. The term glauconitic mica seems appropriate for the Nlound Lake mineral based on the calculated formuia, and Keller (personal com- munication) agrees. The Mound Lake glauconitic mica contains more sodium and less potassium than anv previously reported glauconite.Burst (1958) srrg- geststhat Bonne Terre and Franconiaglauconites represent an end-point potassiumcomposition (Ko.zs based on 016)to which the mineral name M I N ]'RA LOGI CAL NOT T|S glauconiteshould be applied.With diminishing potassiumcontent glau- conitic materials resemblethe . True disordering also becomesevident in the low potash glauconites(Burst, 1958).Roberson and Jonas(1965) show sodium and calciumstabilize the montmorillonite lattice at 10 A even when saturated with ethylene glycol. The Mound Lake material is a disolderedstructure bttt potassiumand sodium have high enoughbinding power so there are no expandablela1'ers of the mont- morillonite type. The potassiumcontent of the Mound Lake glauconitic mica (K6 3e)falls at the Iower end of the range indicated for disordered glauconitesbv Burst (1958).

Tenr-r 2. CoupostrroN or'f-Ban Lexos BnrNrs (Meigs el oI.,1922)

'l' North Barl South T-Barr (Double Lake No. 1) (Double l,ake No. 2)

Dissolved Solids 19 10 21s0 KCl 1-22 t .)o MgClz 2.04 1.t2 NaCI 6.19 767 CaSOr 073 1.93 NarSO4 208 1.40

I Valuesin rvcightpercent represent averages computed from the clata of Meigse/ al., 1922.

A silicatelattice for the formation of glauconiteis provided by mont- morilionite, illite and mixed layer clays which are common in the lacus- trine sediments.Pellets similar to brine shrimp pelletshave beenobserved in thin sectionsof lacustrinedolomites from Mound Lake (Reevesand Parrl', 1965).Similar fecalpellets in the fine-grainedlacustrine sediments probably provided the decaying organic matter for formation of the glauconitic mica pellets. The necessarviron was derived from detrital ferromagnesianminerals in the clastic sedimentsof the iake, the potas- sium and sodium are supplied by the lake brines. Mound Lake brines werenot chemicallyanalyzed because of contaminationbv oil field waste water. Analysesof brines from the T-Bar Lakes, 6 miles southeastof 'Iable 'fhere Mound Lake are shown in 2. is no reasonto believe that T-Bar and Mound Lakes were not similar during the time of glauconite formation. An adequatesuppll'of both sodiumand potassiumis available in the brine fcr glauconiteformation. Discovery of glauconiticmica in lacustrinesediments of piuvial Lake Mound indicatesthat formation of glauconiticmaterials takes place from M I N NRA I,OGICA L NOT L,S 235 montmorillonitic materialsin environmentsother than marine. Caution must thereforebe exercisedin the use of slauconiteas an environmental indicator.

RBlrnr:Ncos

Bt'nsr, J F (1958) Mineral heterogeneity in "glauconite" pellets Am. Mineral- 43, 481- 497 Cr.ouo, P. E , Jn (1955) Physical limits of glauconite formation Am. Assoc. Petrol Geol. 8u11,.39,484-492 DvncnrNxo, M G. .tNn A. Y. Kn.qruNrznva (1956) Casesof glauconite in a continental environment. Mem. Soc.Russe M.in.,Ser 2,85, 49 (Mi.n Abs. 13,287). Fosmn, M. D. (1956) Correiation of dioctahedral potassium on the basis of their charge relations. I/. S. Geol Surrey Bull,. lO36-D,57-67. Kur.nn, W. D. (1958) Glauconitic Mica in the Morrison Irormation in Colorado. Clays ond Clay , FiJth Natl. Conf . Clays Cloy Minuols,1956 Notl. Acod- Sci., Washing- ton, D. C. 'I'exas Mnrcs, C. C , H. P. Bessorr .cNroG. G Sr.eucnrnn (1922) Report on alkali lakes Teros Bur Econ.Geol. 8u11.2234. Rnrvos, C. C, Jn. (1962) Pleistocene lake basins of West'l'exas. GeoI. Soc.Am Spec Poper72,222-223. 'I'exas. - (1963) Subterranean natural brines produce sodium sulphate in West G' ound.W ater. 1, 35-36. -q,NoW.'l' Plnnv (1965) Geology of West Texas pluvial lake carbonates Am. Jour. 5ci.263,606-61 5 RonrnsoN, H. E. eNo E C JoNns (1965) Clay minerals intermediate between illite and montmorillonit e. A m. M inerol 50, 76G7 70. Ser.rrrrn, M. (1949) I{echerches sur la glauconie. Bull Soc. franc. Mineyal.72r 473. in, W. A. Daon, R A. Howrc .lNo J. ZussuaN (1962) Rock-Forming Mi,nerols. Yol. 3. John Wilel' and Sons,Nerv York, p. 39. Te

THE AMERICAN MINERALOGIST, VOL 5I, JANUARY_FEBRUARY, 1966

DEHYDRATION OF DIASPORE A1'WATER PRESSURESFROM 15 to 15,000PSI

JoN N. \\,'ennn, Malerials Research Laboralory, Pennsylaani.a State Unirersity.

The deh,vdroxvlation of well-crystallized diaspore from Chester, Mass. has been investigated by differential thermal analysis at H2O pressures ranging from 15 to 15,000 psi. Experimental techniques and the methods used to process data taken from the thermograms have been described in detail br' \Veber and Greer (1965).