American Mineralogist, Volume 66, pages 201-203, I98l

Ajoite: new data

GnoncBY. Crno Department of Geology, Carleton University Ottawa, Ontario KIS 586, Canada

Abstract

New data showthat ajoiteis triclinic,Pl or PT, a: 13.637,b: 14.507,c = 13.6204,a = 107.16,P : 105.45,y : I 10.57o;Z = 3. The mineralis biaxialpositive, 2V = 80o,a = 1.550,F - :1.583, t:1.641 (inNalight);pleochroic:X:very lightbluishgreen,I Z=brilliant bluish green. {010} cleavageis perfect.The orientation of the principal vibration directionsis definedby the sphericalcoordinates X(26.5', 80o),Y(l l8o, 79"), 2(-104.5', l5o). The ex- tinction angle c:Z on (010) is l5o. Electron microprobe and chemical analysesgave SiO, 41.2,AI2O3 3.81, CUO 42.2,MrO 0.02,FeO 0.1l, CaO 0.04,NazO 0.84, KrO 2.50,HrO (TGA to 1000'C) 8.35, sum 99.07 wt.Vo.The analysiscorresponds to (KoroNaor5,Caa6')(Cu"rt Feoor)ALgsSieooO24(OH)6'3.09HrOor ideally, (K,Na)Cu'AlSieOr4(OH)6'3HrO.TGA showeda two-stagedehydration; 50Vo of the total water was releasedbetween 70o and 425"C and the rest between425o and 800oC.Half of the water is zeolitic in nature.

Introduction are alwayspresent. The termination on c may be ei- or both. Ajoite, first described by Schaller and Vlisidis ther {001} or {203} (1958)from Ajo, Pima County, , was thought to be monoclinic on the basis of optical studies. X-ray crystallography The chemicalformula was given as AlrOr.6CuO. Weissenbergand precessionphotographs show the l0SiO, '5r/zH2O.The publishedX-ray powder dif- to be triclinic, Pl or Pl. The parametersof fraction data, however, indicated a significant the reduced cel.l obtained from these photographs amount of in the analyzedmaterial, the 3.34A and refined by a least-squaresmethod using Gan- reflectionof quartz being the secondstrongest in the dolfi diffractiondata (Table l) arc a: 13.637(5),b = powder pattern with a relative intensity of 25 on a 14.507(4),c :. 13.620(2)4,a : 107.16(2),P = scaleof 100.Thus the reportedanalysis and the pro- 105.45(2),y : 110.57(2)'.The single-crystalphoto- posed formula are likely to be erroneous.A re- graphs display strong pseudo-periodsalong a and c study of this unusual mineral was therefore deemed as reflections with ft not equal to 4n and h + I not worthwhile. equal to 5n are either very weak or absent.This is The material came from the New Cornelia Mine. also evident in the indexed powder diffraction data Ajo, Pima County, Arizona, purchasedin 1965from (Table l) in which most reflectionsare of the type the SouthwestScientific Company, Scottsdale,Ari- withh:4nandhrl:5n. zona. The bluish green ajoite occurs in veinlets and The conventionalDebye-Scherrer powder diffrac- as spraysof fine, prismatic,bladed crystalslining ir- tion photographsshow a strongpreferred orientation regular shapedvugs in monzonite stained in places effect on the 0/<0reflections, suggesting that ajoite by a mixture of hematiteand sericite. crystals possessesa perfect {010} .The Debye- are corlmon in the vugs and minor amountsof barite Scherrerphotographs also show that the d values of are noted. Shattuckiteand ,reported to somediffraction lines, particularly 421,4ll and the be associatedwith the type ajoite material, are char- 0k0 family of lines, tend to vary, presumablydue to acteristicallyabsent. The ajoite crystals(Fig. l), aver- structuraldamage induced by grinding. Comparisons age0.01 x 0.1 x 0.4 mm, are elongatedalong c and of the presentdata with the data from Schaller and flattenedon (010). {010} is the most prominent form Vlisidis (1958)reveal many extra lines in the latter, and {100} and {lT0} are much less prominent but apparentlydue to quartz and sericite. n$-o04x / I | / 0I 02-020I $02.00 20r 202 CHAO: AIOITE: NEW DATA

Table 2. Optical propertiesofajoite

Present Study* Schaller & Vlisidis

0 1.550(r) r. 565 - B 1. s83(r) 1.590 y 1.641 (1) 1.650

2V" neas. 80(1)o 'ca1c. 16-40 680

*ALL neasurenents are for sodim Light at 244C,

extinctionsand interferencefigures. The errors in the orientationof the indicatrix were estimatedto be less than 2". 2V was measuredby direct observationof the optic axeson crystalsoriented to rotate about the optic normal. In white light the mineral is distinctly pleochroic with X: very light bluish green(lscc-Nns color des- - : Fig. l. Scanningelectron microscop€ photomicrograph ofajoite ignation 162), Y Z brilliant bluish green (rscc- showingthe bladedhabit. The width of the large crystal is about NBScolor designation159). Dispersion is indiscern- 0.1mm. ible. The optical data of ajoite are comparedwith the data from Schallerand Vlisidis in Table 2. The ori- Optical properties entation of the principal vibration directionswith re- spect to the crystallographicdirections is shown in The optical propertiesof ajoite were determinedin Figure 2 and is defined by the sphericalcoordinates: sodiumlight at room temperatureon a spindle stage. x(26.5", 90.), Y(llgo, 7go),2(-1045", 15.). The All liquids used were checkedwith extinction anglecAZ on (010) is l5o, confirming the an Abbe refractometer.Crystals previously oriented value determinedby Berman (Schaller and Vlisidis, by X-ray goniometrywere re-orientedoptically using 1958).

Table L X-ray powder-difraction data ofajoite

hk] d(calc.) d(obs.) hk1 d(ca1c.) d(obs.)

010 t2,258 12 25 100 444 2.073 2.O72 020 6 t29 6.72 5 065 2.0421 \t2 5.259| r'uqu 5,24 t 42! z-orsl r21 s.zazl 444 1 , 989 1,989 lt 3 4,522 3 025 I.946 | 946

030 4.086 4,08 r0 454 I .856 1. 858 33t 3 666 3-666 r 075 1.836 1.834 130 3. 391| 3. 381 - 833 1.691 7.692 L0 t.rrt I L6L r.66sl 040 3.065 3.061 10 843 t.eetl c27 2,9A9 2 983 I 853 1. 608| 411 2.839 2-832 8 466 r. ooo/ 414 2.668 2-669 4 416 1.557 1.558 035 2. 590 863 r. srt\ \ 2.581 '. 401 2. s86 t o8o r ,512,

424 2-576 2. 518 6 095 1.4e0t 045 2 455 2,455 72 429 1.488t 005 2 310 2,369 2 439 4ft 2, 304\ 1'119i r.4i7 2.302 . 4r9 L.c/ tt 434 2.342t I .311

055 2.25J\ , )cc r,298 46I 2.251t 1.210 434 2-216 2,2t4 7-246 015 2 160 2.158

Ddta obtained Dith a 114,t: m Gandolfi cme?a, usi.114unentshed c?lstals, CuXa radiatian end NBS silicon as an internal standard. InterLs,Lties Dere estindLed uisually. Fig. 2. Stereographicprqiection of optical and crystallographic elementsof aioite. CHAO: AJOITE: NEW DATA

' Table 3. Chemical analysisof ajoite (IG roNaor.Caa s,) (Cu. r'Feo02) AL essieooo2' 6.09H2O, or ideally, (K,Na)CurAlSirOr' ' 6HrO. AssumingZ to Wt. percent Number of cations be 3, the calculateddensity is 2.951g/cm',in good agreementwith the observeddensity of 2.96g/cm3te' ported by Schallerand Vlisidis. Si0z 4r.2 9.00 Alz0 r 3.81 0.98 Thermal study Cu0 42.2 6.91 a two-stagedehy- Mn0 0.02 0. 004 TGA curves of ajoite showed of the water was released Fe0 0.11 0.02 dration (weight loss).Half the rest between 425o Ca0 0. 04 0.01 between70" and 425"C and quenchedfrom Na20 0.84 0.36 and 800oC.The dehydratedmaterial Kzo 2.50 0.70 1000"C was black and was found to be tenorite Hzo 8.35 12.17 (CuO) by X-ray diffraction. No crystalline silicate Total 99.01 phasewas detected. When quenchedfrom 425oC, af- ter completion of the first stageof dehydration, the mineral regainednearly all of the lost water within 5i02, ALz03, CuO by electron nicroprobe using fluor- phlogopite(S'1, AL) and couellite(Cu) as standnrds 15 minutes. The rehydrated material turned green (Analyst: PauL R, Mainuari,ng). Ather eonstituents by but gavean X-ray diffraction pattern identical to that conuentional aet analysis (Analyst: D, Mah). H20 by ?CA to 1100oC. Nwlcer of cations aexe calculated an of the unheated ajoite. Thus one half of the water the basis of 27 orygen aioms not includ'Lng H2a. presentin ajoite is zeolitic in nature and the other half, releasedbetween 425" and 800oC,is most likely Chemicalcomposition presentas OH. The most probable formula for ajoite (K,Na)Cu'AlSinO'o(OH)u'3HrO. Becauseof the strong cratering effect on the min- is, therefore, eral under the electronbeam only the major constitu- Acknowledgments ents (Cu, Si, and Al) were anaLyzedusing the elec- I thank P. R. Mainwaring for the electronmicroprobe analysis, tron microprobe. For Na, K, and other minor D. Mah for the chemicalanalysis, and J. Bakerfor technicalassist- constituentsthe electron microprobe analysesgave ance.This study was supportedby a grant (A5113)from the Na- poor reproducibility. These elementswere therefore tional Scienceand EngineeringResearch Council ofCanada. analyzedby conventional methods on hand-picked References material, CaO by titration with note, FeO by titra- tion with KrCrrOr, NarO and KrO by flame photo- Schaller,W. T. and Vlisidis, A. C. (1958)Ajoite, a new hydrous metry, and MnO by spectrophotometry.Water was aluminum silicate. American Mineralogist, 43, ll07- I l I l. determinedby TGA to 1000'C. The resultsare given in Table 3. The analysismay be recalculated,on the Manuscript received, June 3, 1980; basis of 27 oxygen atoms per formula, to acceptedfor publication, July 21, 1980.