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Home , Beudantite, Hidalgoite

, A NEW MINERALX Rotnnr L. Surrn, FneNr S. SruoNs,aNo ANcorrNA C. VlrsrDrs, U. S. GeologicalSuraey, Woshinglon, D. C.

Agstnecr Hidaigoite, a new mineral from the San Pascual mine, Zimapan mining district, Hidalgo, Mexico, is a basic sulfate-arsenate of and aluminum, with the formula PbAls(AsOn) (SO4)(OH)6. Hidalgoite is a member of the group and is the arsenate anaiogue of the phosphate hinsdalite and the aluminum analogue of beudantite The unit cell dimensions for both the hexagonal cell and the corresponding rhombohedral cel1 are: ao:7.044; c6:16.99 A; cs/as:2.41; a,t :6.97 A, a:60'40'.

IurnorucrroN The new mineral hidalgoite was collected during a study of the Zima- pan mining district, State of Hidalgo, Mexico. This study was made dur- ing 1948as part of a cooperativeproject between the U. S. Geological Survey,operating under the auspicesof the Department of State,and the Comit6 Directivo para la Investigaci6n de los RecursosMinerales de Mexico of the Government of Mexico. During the courseof this study Simons collected specimens of a peculiar white to light-gray material from a vein in the San Pascualmine and submitted them to the U. S. GeologicalSurvey in Washington,D. C., for identification.This material was examinedin the laboratory by Smith who found one of the constit- uents to be a new mineral. In the preliminary stagesof the laboratory investigations, qualitative chemical tests showed the presence of substantial amounts of lead, aluminum, sulfate ion, and water. Spectrographic examination by K. J. Murata confirmedlead and aluminum and establishedthe presence of -these three elementsbeing the principal metallic constituents. Preliminary r-ray examination by J. M. Axelrod placed this mineral in the family, with a pattern close to hinsdalite. The above data together with the optical properties and specific gravity indicated a new mineral, and additional material was therefore requested for detailed study. This material was obtained through the courtesy of Carl Fries, U. S. Geological Survey, l\{exico City, Mexico. The Zimapan mining district is in the western part of the State of Hidalgo. It is about 200 km. north of Mexico City on the road to La- redo, Texas. The San Pascual mine is on the northwest side of the Barrancade San Jos6some 9 km. northwest of Zimapan. Its adit is along a north-trending dike oI qvartz latite. Both dike and mineralization are probably related to a much larger dike-like body ol quartz monzonite,

x Publication authorized by the Director, U. S. Geological Survey. 1218 HIDALCOITE, A NEW MINERAL t2t9

the NW end of which lies some 300 m west of the mine. The monzonite is intrusive principally into calcareousshale of Cretaceousage; the mine is in overlying fanglomerate of probable Miocene or Pliocene age. The hidalgoite was found in a meter-wide vertical vein in the footwall of an east-west fault that dips steeply north where it crossesthe adit 115 m from the portal. The fault is barren where the hidalgoite-bearing vein cuts it, to the west of the main N-S structure, but to the east it had the largest ore body of the mine, reportedly containing galena, pyrite, , , , and minor amounts of , wulfenite, and .

DBscnrprroN auo Puvsrcer PRopnnrros Hidalgoite occurs in white porous or cavernous to denseporcelain-like masses.In some specimensit has much the appearanceof "bone" -"9- nesite. Much of the material studied is discolored by streaks or blotches of oxide. This is especially true of the more porous specimens. Owing to the fine-grained nature of hidalgoite, cleavagecould not be observed either in hand specimen or under the microscopel , ir- regular in porous specimensto conchoidal in the porcelain-like masses; hardness, 4|; luster, dull; diaphaneity, translucent; tenacity, brittle.

Oprrcer, Dera The fine-grained character of hidalgoite precludes the measurement of any optical properties other than a mean index of refraction. Measure- ments made on several specimens yielded a mean index of refraction ranging from 1.705 to 1.713 for sodium light. Mean n Ior the analyzed material is 1.713*.002 Na. The birefringenceis quite low. In some of the hidalgoite specimens smali spherulitic growths have developed.Some of theseshow extinction crosseswhich, when tested with the gypsum plate, simulate uniaxial positive interference figures.

CnBurcer DarR Hidalgoite is insolublein HCl, HNOa, and HrSOr at one atmosphere pressure. Solution was efiected by heating with 3 ml. of concentrated HCI in a sealedPyrex tube placed in an oven at 150" C. for 3 hours. The standard procedures of chemical analysis were employed. Lead was determined as the sulfate and sulfur as barium sulfate' Arsenic and were determined as the pentasulfide. was precipitated as the sulfide, and ignited to the oxide. Alumina and silica were measured by the usual gravimetric methods, and Fe2O3was determined colori- metrically with KCNS. Total water was determined by the Penfield method using anhydrous sodium tungstate (NazWOr) as a flux' L22O R. L. SMITE, F. S. SIMOITS,AND ANGELINA C, VLISIDIS

The chemicalanalysis and ratios of hidalgoite are shown in Table 1. The calculatedanalysis of PbAIg(AsOr(S04)(OH)ois included for com- parison.Although there is slight departurein ratios from the beudantite structure type, hidalgoite conforms to the formula PbAh(AsOa)(SOd (OH)u. There is minor substitution oI zinc for lead, iron for aluminum, and antimony for arsenic.The analysisshows a departure from the 1: 1 ratio between AsOa (or POa) and SOr ordinarily shown by membersof

Tanr,n 1. Cnnurcer Axervsrs axl Rlrros ol Hmer.corrr:

PbAL(AsOr)(SO,) (OH)u Hidalgoite*

Per cenl Per cent 35 .68 32.U+22322:0.14712 0.88-:-81 .38:0.01081 0.15793

24.25+101.94:O.23788 0.57 + 159.70:0.00357 o.24145 3.02

16.27+229.82:0.07079 0 .20+ 323.52:0 .00062 0.0714r 0.89

SOt 15.03-:-80.07 :O.18771 2.3s

8.64 HrO 9.70+ 18.00:0.53889 6.75

SiOz 0.32 100.00

+ Analyst,A. C. Vlisidis. the beudantite group. I{owevei, a comparable departure may be ob- served in some of the published analysesof beudantite and , rvhere SOris predominant over AsOaand POa,respectively, and in svanbergite, where POapredominates over SO+.Hidalgoite also has a slight excessof water. Part of the iron may be presentas a limonitic impurity. A qualitative spectrographic analysis of hidalgoite by Janet D. Fletcher showedthe presenceof Ca, V, Ti, and Cu, in hundredthsof one per cent, and Mg, Sr, Ba, B, Cr, and Sc in thousandthsof one per cent.

X-nev Dare aNn SpBcrlrc Gnavnv X-ray powder diffraction patterns of hidalgoite were taken using both iron and copper radiation. The iron pattern showedbetter resolutionof HIDALGOITE, A NEW MINERAL I22I

reflections than the copper pattern and thus was used as a basis for cal- culating the unit-cell dimensions. Hidalgoite is a member of the alunite family (used here to include the alunite, beudantite, and plumbogummite groups) on the basis of its qualitative chemistry and its similarity in structure, as observed in *-ray powder patterns, to other members of the family, especiallyalunite and hinsdalite. Indexing of the reflections was therefore accomplished on a Bunn Chart, after an axial ratio approximately that of other mem- bers of the alunite family was assumed. Reflections were present only when -h*kf l:3n, the condition satisfying the conventional setting of the rhombohedral cell indexed on hexagonal axes.Lattice parameters for the larger hexagonalcell were then calculated from the d-spacingsc<-rr- responding to the sharpest difiraction lines and when possiblewhere only one form contributed to the reflection. Calculated d-spacingsfrom these parameters are in good agreement with the measured values. The unit cell dimensionsfor both the hexagonal cell and the correspondingrhom- bohedral cell are: ao:7.04 A; .o: 16.99A; csfas:2.41; a"r,:6.97 A; a:60"40'. The error for ae and c6 is probably within plus or minus 0.02 A of the stated values. The powder pattern was indexed for all spacings greater than I.32. The values for both calculated and observed d-spacings are given in Ta,ble 2 along with the observed intensities and the hexagonal and rhombohbdralindices. The specific gravity of hidalgoite was determined as 3.96 with an Adams-Johnston fused silica pycnometer of 5-cm. capacity. The specific gravity as calculated from the chemical analysis and the unit-cell di- mensionsis 4.27. The discrepancybetween these values is rather large, but explanation might possibly be found in the very fine-grained nature of hidalgoite. Features such as the microcrystallinity, the presenceof spherulites and spherulitic aggregates,and in some specimensthe presenceof mosaicsof minute cracks (simulating mud cracks) suggest that hidalgoite crystal- lized from a very viscous or gelatinous material. Assuming such a condi- tjon it seemspossible that complete crystallization may not have been accomplishedand that there is residual interstitial material that has a lower specific gravity. This condition might also explain the slightly higher water content.

Assocr,lrpo MrNnners The material available for study was collected primarily for the pur- pose of obtaining enough of the new mineral for chemical analysis, and therefore the associatedminerals are probably inadequateiy represented. 1222 R. L. SMITH, F. .'. STMOil.S, AND ANGELINA C. VLISIDIS

Trrr-l. 2, X-nnv Pownun D,lra lon Hmnrcorln Iron Radiation,Manganese Filter, I:1.9373 A EfiectiveCamera Diameter 114.59 mm.

d (measured) d (calculated)

1011 100 .) - /{t 0003 111 5.66 0r12 110 4.96 4.95 1014 2ll 3.49 tr20 101 3.51 ?\? 0221) 1l1l 13.oo 1123f 2ro, 2.981 12.9e0 0lIsJ 'rJ1l 12.968 )ir) 200 2.864 2.869 0006 222 2.830 2.832 0224 220 2.477 2.477 2t3l 201 2.282 2.283 2@s 311 2.269 ro17 322 2.257 2.255 1232 2rl 2.226 a a1l It26 32r 2.204 2.206 so3-oI 21T\ 2.O27 12.032 21341 3r0I \2 02s 0118 332 2.009 2.006 03331 221]' (r.9r3 3033| 300I 11.e13 r23s) 320) [1.907 0227 331 1.899 0009 333 1.888 2240 202 t.,/or r.7ffi 2028 422 1.746 r.743 1341\ 212\ 1.681 1r.683 2243( srl j u.681 .67| 2137\ 421i 1.667 -[1lr rrzel 43?l .664 3r42 301 1.658 3036\ 411I I .651 Ir.6sr os\6l 3301 \1.6s1 10T.10 433 1.638 r.637 ??T] 1344\ I .570 I1.s7r 1238i L?1 ( u. s62 .518 4041I 3I1I 1 I1 sr4sl 410( .514 11 .514 0442 )'rr\ \ rlr.497r1.s00 o1T.11 | 4431 1.496 2246 ) 420) |.1.49s o22'10 M2 r.484 t.4u 4044 400 1.434 1.435 000.12 M4 I .418 1.4t6 325r) 302l lr.3e4 33II |1.3e1 430[ )r .387 522( 1.386 I 1.383 Mll | 1.383 3r2) [1.380 s33I t.370 Ir.378 5321 l1 .368 .330 4150\ 312\ 1.330 t1 32541 4111 11.32e 3148 521 1.323 HIDALC,OITE.A NEW MINERAL 1223

The following minbrals were observed in the specimensstudied: limo- nite, hydromica, orthoclase,tourmaline, beudantite, and a mineral tenta- tively referred to as ferrian hidalgoite.

Limonite occurs as a staining in streaks and blotches throughout most of the hidalgoite. In the highly porous and cavernous specimensit may be found concentrated in small earthy or resinous masses.

Hydromico and Orthoclose A sericitic mineral identified as a hydromica and an alkalic feldspar, here called orthoclase,were identified on the basisof their optical proper- ties. These two minerals occur either together or separately as fine- grained aggregatesin pockets in hidalgoite and are most abundant in the limonite-rich cavernous areas. They appear to have formed earlier than hidalgoite.

Tourmaline Tourmaline was observed in only one specimen, where it occurs in mats of greenish-gray needles associated with orthoclase and hydro- mica. This mineral was identified by its optical properties and by *-ray. The optical propertiesate as follows: indicesof refraction, e:t.62+.002 and co:1.643+.002;pleochroism, 6:yellow utr4 ,:pale blue. The in- dices of refraction were measured using white light.

Beudantite A dark brownish-green mineral was found in exceedinglysmall quan- tity on two specimensof hidalgoite.On the basisof its optical properties and association, it was identified as beudantite. The optical properties that couldbe determinedare: mean n l.95,low to moderatebirefringence, anomalous blue interference colors, lemon-yellow to pale-yellow pleo- chroism. An x-ray powder pattern was obtained of this mineral which shows a very closesimilarity to corkite from Beaver County, Utah. The principal difference is the larger cell size of the beudantite.

Ferrian hidalgoite A mineral tentatively referred to as ferrian hidalgoite occurs in close association with beudantite and hidalgoite. It occurs in small veinlets and spherulitic growths in hidalgoite and in narrow zones surrounding crystals and spherulites of beudantite, separating them from the hidal- goite matrix. This material is light green in color, has a mean index of 1224 R. L. SMITH, F. S. SIMOTS, AT{D ANGELINA C. VLISID]S refraction of. I.79, and a low . Enough of this mineral was separated to obtain an r-ray powder pattern. This pattern is very close to hidalgoite, but differs in having a slightly larger cell and in the relative positions of a few lines. These few lines show a slight departure from hidalgoite and seem to be related to correspondinglines on the pattern obtained from the associatedbeudantite.

Acrwowr,nncMENTS The writers are indebted to Joseph J. Fahey for aid and advice during the making of the chemical analysis. Especial thanks are due to Donald H. Richter for aid in the *-ray procedure and calculations and to Mrs. Robert L. Smith for aid in the calculations.

RrlnncNcrs

Hrnonrcrs, Srrnr.rNc B. (1937), The of alunite and the :,442. M'ineral., 22, 77 3-7 84. Pansr, Alor,l (1947), Some computations on svanbergite, woodhouseite, and alunite: Am. Mineral.,32, 1G30. Per-ecnn, C., Bnnlr.nN, H., exo FnoNorr., C. (1951), Dana's System of Mineralogy, Seventh Edition, Vol. II, New York, John Wiley and Sons, Inc. SruoNs, FnaNr S., Awo Maens, Enuanoo, Geologv and ore deposits of the Zimapan mining district, Mexico (in preparation).