American Mineralogist, Volume 61, pages 189-192, 1976

Stringhamite,a newhydrous from Utah

Jnuss R. HINnunN Department of Geology and Geophysics Uniuersity of Utah, Sslt Lake City, Utah 84112

Abstract

Stringhamite,CuCaSiOo.2HrO, is a new mineral speciesfound in the Bawana mine at the southern end of the Rocky Range, Beaver County, Utah. The mineral occurs as crystals and botryoidal fillings in a diopside-magnetite skarn and is associatedwith thaumasite, tenorite. kinoite. and . The spacegroup is P2r/c wtth ao : 5.028,b, : 16.07,co : 5.303A,and B : 102.58'.The five strongestpowder diffraction lines are: 8.05 (35), 3.928(34),3.236 (39),2.768 (100)' and 2.523(40\. Crystalsare monoclinic and are dominated by {011}and {l0l}, with {010}and {ll1} also present.The coloris azuriteblue and the mineralis transparentto translucent.Crystals are biaxial(+) witha = 1.709(lightgrey blue), 0: 1.717(light blue), andT : 1.729(dark blue); 2V.^r.: 80'; X -- b and Y A c : 2.5'. The mineralis namedin honorof BronsonF. Stringham(1907-1968), latechairman of the Departmentof Mineralogyat the Universityof Utah.

Introduction more recentlydeveloped into the Bawana open pit. A more completediscussion of the geologyand miner- During examinationof specimensof diopside-mag- alogy of the areamay be found in Hintze and Whelan netite skarn collected from the Bawana mine, near (1e73). Milford, Utah, a mineral resembling was Crystalsof stringhamiteusually occur with crystal- found associated with thaumasite. Further in- line thaumasiteon fracture surfacesin the diopside- vestigationof the mineral indicatedthat it was a new magnetite skarn. Small radial aggregatesof minute copper calcium silicate.Though severalof the speci- crystalsalso occur with bornite and chalcopyritedis- menscollected in 1969contained this mineral, it was seminatedin granular diopside.From examinationof not until recently that single crystals suitable for the limited number of specimensavailable, it seems spacegroup determination were located at the type that stringhamite formed by the reaction of copper locality. bearingsolutions with diopside.Other mineralsasso- The mineral is named in honor of Bronson F. ciated with stringhamiteare tenorite,kinoite, and an Stringham(1907-1968), late chairman of the Depart- undescribedsilico-carbonate of copper and calcium. ment of Mineralogy at the University of Utah. (Love- Although over twenty specimenscontaining string- ring, 1970). The speciesand name have been ap- hamite have been found, there is probably not more proved by the Commission on New Minerals and than a gram of the mineral present in the samples, Mineral Names,IMA. and only a few milligrams were recoverablefor study'

Occurrence Chemistry

Stringhamite is found in a diopside-magnetite The composition of stringhamiteis primarily cal- skarn formed at the contact of a quartz monzonite culated from electron microprobe analyses.Initial with Toroweap limestone(Permian) in the Bawana qualitative analysis indicated that copper, calcium, mine, 4 miles northwest of Milford, BeaverCounty, and were the only major detectableelements. Utah. This deposit was originally worked as the Old Quantitativeanalysis was performed usingcrystals of Hickory mine in the early part of the century and shattuckite and dioptase as standards for copper. 189 190 JAMES R. HINDMAN

Other elementswere measuredusing analyzedpyro- TnsLr I . Electron microprobe chemical analysisof stringhamite xenes,olivines, and feldsparsas standards. Water was determined on a 2 mg sample using cuo at.es1 .zz1' 33.41( .82) 34.10(-89) 34.32 thermogravimetricanalysis. A weight loss 12 per- Cao 24.64( .28) 2s.40( .58) 26.97(.80) 24.20 of r4s0 .s4(.12) .01(.04) .e4(.97) cent was measured. After heating to 900'C the final Feo .23( .04) .77( .3s) N.D. A1203 .03(.04) .0i (.13) .07(.06) decomposition product was identified by X-ray dif- si02 28.42(2.i1 26.95(5.48) 27.46(.67',) 25.93 nzoli. 14.s2 13.39 10.46 t5.55 fraction as a mixture of wollastonite and tenorite. H;o'* tz. J- | )ErrngnamrEe; ootryoroaI lncrustatton. Initial examination of 100microprobe data points 5-2 Stringhamite;crystal fragments. yielde&a s-3 ltlineralF, Crestmre Quarry,California. formula of Cu.roCa.r,SiOs.E.2.llHrO. This * Standarddeviations are given in parenthesis. formula was based H20 determinedby difference. on using the difference between *** H20 detemined by themogravimetric analysis. the sum of analyzedoxides and 100percent to obtain a value for water. Magnesium was extremely vari- beenhand picked for purity. The spectrais able, with MgO ranging from 2.3 percentin massive shown in Figure 2.The presenceof (HrO) was verified peaks material to trace amounts in crystal fragments. Con- by at 3150 2890, peaks sequently,26 of the initial set of data points having and cm-l, while the other are indicative of the lowest magnesium content were used for the cal- SiO;'. The density culation of copper, calcium, and magnesium.An in- of stringhamite was measured on 100-200 mesh grains which dependent set of 104 data points was used in the had first been concen- trated magnetically.Due determination of iron, aluminum, and silicon. The to similaritiesin both den- sity properties, resultsof the analysesare presentedin Table l. and magnetic pure samples of stringhamitecould only be obtained by hand sorting from a concentrate of approximately 20 percent Crystal geometry and X-ray diffraction stringhamite and 80 percent diopside. Repeated measurementsof densitiesof Weissenburgphotographs were taken of a crystal stringhamite-diopside suspensionsin methylene iodide indicates rotated about its a- and b-axes. Systematic extinc- that the density of stringhamitespans tionsof (0k0),k :2n t l; and (ft0l),I :2nI l;were a range of 3.16 to 3.18 gm/cms at 20'C. This measured density is appre- observedindicating a spacegroup of P2r/c. Several ciably lessthan the densityof 3.67calculated crystals were examined to find one suitable for in- from X- ray data. Becauseof this discrepancy, tensity measurements,but all of the crystalsexam- all the material used for thermogravimetric, ined were multiply twinned. Reflectionswere made infrared, and density de- up by as many as 13 closelyaligned segments. terminations was veriffed by X-ray diffraction before the determinations A powder pattern was made using a Debye-Scher- were made. The rer camerawhich had brasspins placed to cast fidu- density and measured refractive indices cial marks at 0 and 180 degrees.The pattern was were deciding factors in choosing a final formula of . indexed using cell parameters from the Weissenberg CuCaSiO* 2H2O.If the TGA value for water of l2 percent photographs, and these parameterswere refined with is used in calculating the chemical formula, a formula of CurCarSiros. a least squaresfit of 19 high angle lines. The cell 3HrO would be obtained.A parameters thus obtained for stringhaffiite : are: ao T r,stB 2. X-ray data for stringhamite* 5.028(5), bo: 16.07(2), co:5.303 (6) A, andp : 102.58' (9). The calculatedcell volume is 418.204s. The X-ray powder pattern is presented in Table 2. 4.884 2l 100 4.907 132 4.687 20 ilo 4.693 081 4.370 9 021 4.351 260 4.182 20 -Iil120 4.-188 152 Physical and optical properties 3.928 34 3.905 251

3.618 21 130 3.618 1.657 lt 162 I .656 Stringhamite is deep azurite blue in color, with 39 t3t 3.218 l.614 23 202 1.614 2.768 100 r3l 2.764 I .595 14 33r | .592 fragmentsbeing transparent 2.690 l0 to translucent.Crystals 150 2.689 '|1.551 19 281 1.549 are biaxial(+) with = : : 2.609 t9 002 2.588 .530 5 271 1.530 a 1.709,B 1.717,and 7 40 l4r 2.516 1.482 l9 332 1.482 1.729 for sodium light;2V"^r" : : '14 80o, X:b, Y A c 2.48'l 022 2.463 1.429 143 1.427 2.5'. The : a.4Jl t8 210 2.425 L 385 262 1.382 mineral is pleochroic with a light grey 2.344 'I : l8 220 2.347 . 347 291 1.347 blue, p light blue, 7 : dark blue. 2.222 16 231 2.2',t4 t.334 351 I .33i 2.O89 l5 112 2.090 '|1.310 083 1.309 The infrared spectrumwas obtained from a potas- it 211 sium bromide disccontaining stringhamite which had STRINGHAMITE, A NEW HYDROUS COPPER CALCIUM SILICATE l9l

Tlnre 3. Comparisonof stringhamiteand Mineral F

8.049 35 020 8.013 32 020 4.884 2l 100 4.928 20 100 4.687 20 ll0 4.69',1 l8 ll0 4.370 9 02] 4.363 14 021 4.182 20 120 4.220 5 120 3.928 34 Tlt 3.951 3l l ll 3.6',1I 21 r30 3.611 23 130 3.236 39 T3l 3.242 s5 T3l 2.768 100 l3l 2.770 100 l3l 2.344 18 220 2.355 22 220

2.003 1I 080 1.996 16 080 : = 1.875 17 081 1.876 35 081 Frc.L Typicalhabit of a stringhamitecrystal. d (l0l); w ',l 260 = I .805 I 260 'L7I3l.8ll 12 (0ll);b = (010);0 (Tl1). 1.729 I 251 l0 251 ].614 23 202 1.602 62 202 I z8r mean refractiveindex was calculatedfor both for- 'II .551 19 281 .530 5 271 I .521 18 '143271 mulas,using specific refractive energies listed in Lar- 1.429 l4 143 1.437 20 1.347 I 291 senand Berman(1934) and Mrose(1965). Using a are densityof 3.I 8, the calculatedz's are I .701and I .685 respectively.The measured0 of 1.717for stringham- extent.This typicalhabit is shownin Figurel. Size ite is in good agreementwith the first valueof 1.701. doesnot exceed0.lmm for crystalsthus far observed. Severalcrystals of stringhamitewere examined by scanningelectron microscopy. One of thelarger crys- Relationshipto "Mineral F" tals had a core of angular crystal fragments.The resultingvoids might accountfor the low measured In 1943A. O. Woodfordassigned the designation density.Because all of the reflectionsexamined on "Mineral F" to a mineraloccurring as crystalline singlecrystal photographs were composed of mul- blue films coatingjoint planesin rock at Crestmore tipletwin segments,it is assumedthat this twinning is Quarry, RiversideCounty, California (Woodford, presentin all of the stringhamitestudied. 1943,p.362).A specimenof MineralF wasexamined by X-ray diffraction.The specimenconsisted of blue Crystal morphology films on coarselycrystalline calcite. The powderpat- tern obtainedis comparedto the Bawanamaterial in Individual crystalsare rare. is strongly Table 3. An electronmicroprobe examination of monoclinicwith (0ll) and (101)being the dominate Mineral F alsoyielded results essentially identical to forms and (010) and (Tll) presentto a minor thoseof stringhamite.

WAVELENGTHIN MICRONS 67 12

t9 260 o o o = o 140 G F

waveNuueen(cM-1) Ftc. 2. Infrared absorption spectra of stringhamite. t92 JAMES R. HINDMAN

Stringhamite from Christmas Mine, Arizona manuscript and offered suggestions and criticisms. An especial acknowledgmentis due John F. Clarkson whose keen powers of Additional information on stringhamite from observation during a field trip in 1969 initiated this study. Ac- another locality was obtained too late for adequate knowledgement is made to the donors of the Geological Research discussion.Sidney A. Williams, working independ- Fund, administered by the Department of Geology and Geophy- ently on material from the Christmas Mine, sics,University of Utah, for partial support of this research;and to the Mineral Leasing Fund of the College of Mines and Mineral measuredthe following cell parameters:a0 : 10.04, : Industries,University of Utah. bo 16.12,co : 5.34 A, and B : 102.91'. The stringhamitefrom Arizona doesnot contain measur- References able magnesium and has a unit cell double that of the type material. This is indicated in the powder pattern by a line of 3.037 A which is not present Hrrrzr, LrHr F., nro Jevrs A. WHer-eu(1973) Geology of the in powder patterns of the Bawana stringhamite. Milford area.Utah Geol Assoc.Publ. 3. Llnspu, EsernS., lNo Hennv BenueN(1934) The microscopic of the nonopaqueminerals, 2nd Ed. U.S. Acknowledgments determination Geol. Suru Bull 8/,8, LovenrNc,T. S. (1970)Memorial of BronsonF Stringham.,4rr. The writer wishesto acknowledge severalindividuals whose help M ineral., 53, 60'7-614. made this study possible.W. P. Nash assistedin obtaining and Mnosr, Mlny E. (1965)New specificrefractive energy values for interpretingthe microprobe data. F. W. Cagle made availablethe CuO and Sc"Oa.Am Mineral.,50,288. facilitiesof his crystallographylaboratory. R. J. Neustadt was of WoouRono,A. O. (1943)Crestmore minerals. Diu. Mines invaluablehelp in obtainingsome of the X-ray data A lan Eastman Calif. Rep.39,333-365. assistedin obtainingthe infrared data,and Eric Cather,of the U.S Bureau of Mines, made facilities available for the thermogravimet- ric analysis A. O. Woodford kindly examined the specimen of Manuscript receiued,Augusl 25, 1975;accepled Mineral F to verify its identity, and J A Whelan reviewed the for publication,Nouember 4, 1975.