THE AMERICAN MINERALOGIST, VOL. 43, NOVEMBER_DECEMBER' 1958

AJOITE, A NEW HYDROUS ALUX{rNUII SILICATE*

W. T. Scu,uLERAND ANcBr-rN.q. C. Vrrsrors, U. S. Geological Suruey, W ash'ington25, D. C.

ABsrRAcr

Ajoite is a nerv bluish-green hydrous aluminum copper silicate from Ajo, Pima County, ,\rizona. It rvas collected by Harry Berman in 1941 and recognizedby him at that time as probably a new . Mostly massive, a few cavities contain platy crystals or laths elongated parallel to c and flattened parallel to {010}. It is biaxial positive with indices of refractiona:1.565,8:1.590,'y:1.650, +2V:68",X:b,ZAc:15'.Thespecificgravity is 2 96. The r-ray powder pattern could not be related to that of any other copper silicate. The strongestlines are: 12.4(100), 3.34 (25),6.19 (9), 4.12 (9),3 09 (9). Examination with an r-ray diffractometer showed that neither medmontite nor any montmorillonite group mineral can be present Chemical analysis yielded the formuia AlzO: 6CuO 10SiO: SiHzO' Ajoite is not related to any of the severalimpure mixtures oi copper silicatesand aluminum . INrnolucrroN Specimensof a bluish-greencopper aluminum silicate,named ajoitet after the locality Ajo in northwesternPima County, , were col- lected by Harry Berman of Harvard University, in August 1941 to- gether with specimensof dark blue . Preliminary examina- tion by him, chiefly optical, indicated that the greenish mineral was probably a new species.It had been planned by Berman and Schallerto collaborateon the study of this new mineral and possiblyto extend such a collaborativeinvestigation so as to includeall the known coppersilicate minerals,a plan nullified by Berman's untimely death in 1944. It is a tribute to Berman's keen perceptionthat his earlier prediction of a new mineral has beenborne out. The two gram sampleof massiveajoite preparedfor analysisby Ber- man was further purified by hand-picking the few remaining small spherulites of blue shattuckite enclosedin the greenish ajoite. The resulting purified sample was analyzed by Angelina C. Vlisidis after a pycnometer determination of the specific gravity and a preliminary spectrographicanalysis. Later, the entire collectionof thesespecimens was forwarded by Prof' Clifford Frondel (Harvard University) for completion of the study. A secondsmall sample of massiveajoite was preparedfrom thesesamples for the several qualitative tests made, checking the optical determina- tions, and taking additional r-ray powder-diffractionpatterns.

* Publication authorized by the Director, U. S. Geological Survey. t Pronounceclah'ho ite. tl07 1108 W. T. SCHALLER AND A. C ITLT.qIDIS

AssocrlrroN N{ostof the ajoite is compact massive,resembling some deeper colored chrysoprasein color and specimenstructure, and is intimately mixed with dark blue shattuckite and white massive . Occasional small cavitiescontain aggregatesof elonagedplates of ajoite, a millimeter and less in length. Other less abundant associatedminerals observed are minute pearly scalesof sericite, white powdery quartz, , very pale blue altering shattuckite, limonitic stains,and on one specimenmassive co:richalcite.Berman (letter to W. T. Schaller,dated June 12, 1942)also noted the presenceof this mineral (he referred to it as "higginsite") perchedon the new copper silicate. As observedin a thin section,the relation between ajoite and shat- tuckite seemsrather indefinite, but, in general,the greenishajoite ap- pears to have replaced the shattuckite, as noted by Berman. On the other hand, the presenceof small seamsof shattuckite, grading down in size to isolated minute spherulites,suggests to one of us (W.T.S.) that shattuckite may be forming at the expenseof the ajoite and later than it.

Puysrcer, AND OprrcAr, PnopBnrrns In color ajoite approaches very closely Ridgway's Venice green, Plate VII,41. BB-G, about 75 per cent greenand 25 per cent blue. A letter, dated June 12, 1942,from Berman to Schaller,stated that the light green,lathlike ajoite found replacing the shattuckite is mono- clinic, elongatedparallel to c and flattened parallel to {010}. Berman determinedthe indicesof refractionto be a:1.565, B:1.590, 7:1.659, with a birefringenceof 0.085.From theseindices 2V is calculatedto be 68'. Optically positive, X:b, ZAc:15o. These values have been con- firmed by Schaller. The specific gravity of the analyzed sample is 2.96 (pycnometer). . X-Ray Powtpn-DrnlnacuoN Dara X-ray powder-diffractionpatterns (films 5759, 12557,and 12559) of the massive analyzed material are identical with those taken of the bet- ter crystallizedmaterial (films 5757 and 5757A) on which Berman made his optical determinations.The measuredpowder data listed in Table 1 were obtained from a pattern (film 12559) taken by Mary E. Nlrose, U. S. GeologicalSurvey, with a Debye-Scherrercamera (114.59 mm. diameter) using the Straumanis technique, with CuKa radiation (Ni filter), I:1.5418 A. pitm 12557is reproducedin Fig. 1. Couposrrrow The analysis of the small sample of ajoite first purified by Berman and later by Schaller, guided by prior spectrographicexamination, AJOITE, A NEW ALUMINUM COPPER SILICATE 1109

Tesr,B1. X-nlv Powonn-DrrrnectroNDera lon A;onr rnou A1o,AnrzoNe (anall,zedmaterial; film 12559) CuKa (Ni filter),I:1'5418A Cameradiameter 114.59 mm.; cutoff at 17.7r\ Correctedfor shrinkage(by M. E. Mrose)

Il d(meas.) d(meas.) d(meas.)

100 t24 1 2.37 I ..)/ / t 9 .98 ? 2.30 1.555 9 6.19 3 2.28 1.540 1 5.19 3 2.26 1.527 1 4.99 1 2.21 1.506 3 4. .53 1 2.16 1.489 3 4.25 1 2.12 2 1.480 () +.12 1 2.08 2 1.449 1 3.87 1 2.02 I 1.416 1 3.73 1 2.00 1 1.384 4 3 .48 1 1.978 1 1.373 2 3.40 1 1.949 \.J+l 25 3.34 1 1.862 1.333 9 3.09 I 1.841 1.309 .5 2.93 3 1.818 | 296 o 2.79 1.802 1.278 3 2.66 1.77s 1.268 2 2.59 1.752 1.250 3 2.55 2 1.672 1.228 4 z-51 I 1.642 1.198 6 2.46 I 1.617 1.184 I 2.43 I 1.595 1.181 Plus many more weak lines

I Intensitieswere obtained bv visualcomDarison with a calibratedintensity strip based on log y'2. showedthat ajoite is a hydrous aluminum copper silicate with the for- mula AlzOa.6CuO. lOSiOr. S*HzO. The spectrographicanalysis by K.J. IIurata, U. S. GeologicalSurvey, showed: XO Si, CU X Al, As, Ba O.X Ca, Fe, Mg, Mn, Ti O.OX Na o ooxB Not founcl: P, Pb, V, Sn, Be, Bi, Cr, Ge, Li, Sb, Zr, Zn

The resultsof the chemicalanalysis are given in Table 2.The formula derivedtherefrom is AI:Oa.6CuO. 1OSiOz'5+HrO. Ajoite is readily decomposedby acids,leaving a coherentwhite mass W. T. SCIIALLER AND A. C. VLISIDIS

Frc. 1. X-ray powder-difiraction pattern of ajoite. Cu Ka, Ni filter. of hydrated silica with small unattacked particles of blue shattuckite scatteredthrough it. At room temperature,with 1: 1 HCl, decomposition takes placeovernight. In 1: 1 NHOB severaldays are required.When the mineral was treated with NH+OH at room temperature overnight, no reaction was noticed. The role of arsenic and barium in the mineral is not definitely known, but the arsenic is consideredas due to admixed conichalciteand the barium to barite as the ratios of BaO (0.0033)and SOa(0.0029) are very close.Based on the determinedpercentages of AszOrand of BaO, 3 per cent of conichalciteand 0.76 per cent of barite are deductedas impuri- ties. The value siven for FeO is for total . Trr;n 2. ANll.vsrs or Ayorm (by A. C. Vlisidis)

Deducting Remainder Analysis Ratios Ajoite and barite

sio: 45.90 45.90 0.7642 0.7642 10.10 10 xl.01 CUO 33.90 32.98 .41461 FeO .78 .78 .010eI MnO .10 .10 .0014[ .M94 5.94 ( 6 X0.99 Mgo .66 .66 .0164 CaO .99 .34 .006lJ BaO .50 AlzOs 7.30 7.30 .07161 0.97 I .0736 1x0.97 TiOz .16 .16 .oo2o) AsrOr 1.33 SO: .23 H:O- 2.55 2.55 . r+r-rI 5.49 I .4151 5+X1.00 HrO+ 5.03 4.93 .2736)

99.43 95.70 2.96 AJOITE, A NEW ALUMINUM COPPERSILICATE 1111

Determinations of the water content of ajoite were repeated on two other small samplesof the material, (1) a secondsmall sampleprepared by Berman and (2) a small sampleprepared by Schaller.The resultsob- tained are: (1) (2) Analyzedsample HzO- 1.85 1.92 2.55 HzO+ 6.s4 5.03

Total HzO 7.54 8.26 7.58 If the valuesof (2) are substitutedfor thosegiven in the analysis.then the ratio of the total H2O becomes5.96, very closeto 6.

RBre,rroNs ro OrHER Copppn Srr-rcarrs John C. Hathaway of the U. S. GeologicalSurvey examined ajoite with an r-ray diffractometer using both air-dried and ethylene glycol sat- urated samplesand was unable to detect any montmorillonite group mineral. X-ray examination of ajoite heated at 400oC. showedno col- lapsein the structure. These results demonstratethat neither medmon- tite, a copper-bearing(20.96 per cent CuO) clay of the montmorillonite group, nor any other montmorilionite group mineral can be present. Ajoite is not closelyrelated to any of the severaldescribed hydrous cop- per aluminum silicatessuch as traversoite,a light blue "new variety of chrysocolla"with 21.84per cent AlzOrand 32.84per cent H2O, believed to be a mixture of chrysocollaand gibbsite;or pilarite with 16.9per cent AIzOrand 21.7per cent H2O,or to similar material from Utah with 10.78 per cent AlzOrand 25.76per cent II2O, the alumina being ascribedto ad- mixed allophane;or to any of the severalprobably impure bluish chryso- collaswith small amounts of AlzOa.A mixture of chrysocollaand alunite (or natroalunite) has also been described.\Iost of these chrysocollas containing appreciableamounts of alumina are probably mixtures of typical chrysocolla(essentially CuO.SiOz. 2HrO) with other copper free minerals. Alumina is commonly present in these mixtures as hydrate, phosphate,sulfate, or silicate. All these mixtures contain much more w lter thcn is presentin ajoite.

AcrNowrnocMENTS Our appreciation is expressedto Nlary E. X,Irosefor powder-diffrac- tion work, to K. J. Xrluratafor the spectrographicanalysis, and to John C. Hethaway for his kind assistance. lf u,nusuipt receitsedMarch 12, 1958.