ADAMITE FROM THE OJUELA MINE, MAPIMI, MEXICO* Menv E. MnosBl wrrn Norns oN rHE Occunnpwce sv Dew E. Mevpns2 eup FnnNcrs A. Wrsn3 Alsrnect Adamite of unusually pure corrposition is described from a new locality, the Oiuela mine at Mapimi, Durango, Mexico. A chemical analysis is given together with measure- ments of the morphological axial rutio (a:b:c:O 9753:1:0.7055), the unit cell dimensions (os:8.30, bo:8.51, co:6.04 A), the specific gravity (4.435) and optical constants (X :1.722,Y:1.742, Z:1.763,2V (meas.)88"1-2'). Analysis gaveZnO 56.78,AsrOs 38.96, SiO, 0.26, H:O 3.53; total 99 53. Spectrographic analysis also revealed Cu (-g'1;, p5 (-0.1), Fe (001-0.1), Mg (0.01-0.1),Al (-9.91;, Ca (-6.91;, Ag (0.001-001) and Ga (-0.001). Cnvsrerr,ocRAPHY Most of the crystals of Mapimi adamite occur merged together as radiating crusts or as fan-shaped rosettes on a matrix of limonite. A few Frc. 1. Adamite crystal from Mapimi showing all the forns observed. single-crystals,however, were found. The crystals are elongated parallel to [010]. Most crystals were attached at one end of the &-axis;only three doubly terminated crystals could be found. These indicated holohedral symmetry. A test for piezoelectricity by the cathode-ray oscilloscope method gave negative results. The crystals range in size from j mm. to 8 mm. along [010]. The crystals are rather simple in habit. The form d{1011is dominant and is truncated by t1120\ and ml 110]. On some crystals the prism hl2I\l occurs,but only as very small faceswhich gave poor signalsdur- ing goniometric measurement,and D{010} was observedin several in- stances.The faces in the [010] zone are highly striated parallel to [010], producing a train of signals which made accurate measurementsimpos- * Contribution from the Department of Mineralogy and Petrography, Ilarvard Uni- versity, No. 298. 1 Boston University, Boston, Massachusetts. 2 Harvard University, Cambridge, Massachusetts. 3 American Smelting and Refining Co. M9 450 MARY E. MROSE, DAN E. MAYERS AND FRANCIS A. WISE sible. A somewhat idealized drawing showing all of the forms observed is given in Fig. 1. Although a great number of crystals were carefully examined, only nine of the very best of these were selectedfor measurement (Table 1). TesLE 1. Aoeurrl' : Mnasunno eNo Cer,culamn ANcr-ns No No Measured Range Forms of of Qual- itv* XIs M il"'l6zpz 1 1 VS c 9 18 M B 9 18 S D 45"11,-46 32 9 14 VS r, 63 42 -64 t4 9 36 L B 53022'-5+o59' * A equals first quality The linear elementsderived from these measurements(a:b:c:0.9753: 1:0.7056) are identical with those derived from c-ray Weissenberg measurementson the samecrystals (a: b: c:O.9753 : 1 : 0.7055). A number of other investigators have reported elements for adamite from other localities and these are listed in Table 2. TnrrB 2. ReponrBo Monpnor,ocrclr, Elrupxrs or Areurre Investigator Locality Axial Ratio 1. Des Cloizeau(1878) Chanarcillo, Chile dibie:0 .9733i1:0. 7158 2. Aloisi (1909) Mte. Valerio, Italy a:b:c:0 .9736'.1:0. 7013 3. Staples(1935) GoId Hill, Utah oib:c :0.97 42i1:0. 7095 4. Mrose (1948) Mapimi, Mexico a:bic:0 .975311 :0.7055 5. Rosickf(1910) Thasos, Turkey atb.c :0.97 64iI i0.7049 6. Ungemach(1921) Laurium, Greece ai b: c : 0.977 01 1 t0.7 124 7. Des Cloizeauand Lacroix (1e10) Laurium, Greece aibic:o .9784:.l:0.7ll7 8. Kukharenko(1939) Northwestern Balkhash region (lilac variety) a;btc:0 .9787:l:,0 .7128 9. Palache(priv. comm.;1921) Laurium, Greece a:bi c :0.9812i1 :0. 7108 10. Laspeyres(1878) Laurium (emerald-green; cuprian) aibi c:0.9958i1 :0. 6848 Laurium (colorless) a:btc :0.99s8i I io.717 6 11. Murdoch (1936) Chloride Clifi, Calif. (colorless) aibic:0.996:1:0.718 The wide variation observed appears to be due largely to the poor quality of the measured crystals. In part, however, the difierencesmay be due to variation in chemical composition such as substitution of Cu or Co for Zn or of (POa)for (AsOn),but no definite correlations could be ADAMITE FROM MAPIMI, MEXICO r+J -t established.Laspeyres (1878) has shown that the angles of the adamite crystals from Laurium vary measurably with the presenceof Cu in sub- stitution for Zn. The arithmetical averageof the linear elementsreported, after eliminating those of Laspeyres (1878), Murdoch (1936) and Des Cloizeau (1878), which are relatively far out of line with the others, is a:b:c:0.9769:1:0.7086.An angle-tablefor the forms observedon the Mapimi crystals calculated for these elementsis given in Table 3. Tasrn 3. AlAltrr: ANcr.r Teslr Orthorhombic; dipyramidal-2 /m 2/m 2/nt a:bic:0.9769:1:0.7086; po:qoiro:o.7254:0.7086:1 Qt:r i fu: 0 .97 69 : 1. 37 86 : | ; rzifzi qz: | .4ll2 : I 0236i I Forms: Q p:C 6r pl--A 6z pz:B b 010 0'00' 90000, 90'00' 90'00' 0'00' t 120 27 06+ 90 00 90 00 62 53+ 0'00' 27 06+ m 710 45 40i 90 00 90 00 M 19+ 0 00 45 40' h 2r0 63 58 90 00 90 00 26 02 000 6358 d r0l 90 00 35 57; 0 00 54 02+ 5402+ 90 00 Pnvsrc.q.rPnoprnrrrs Cleavage[101] good. The {010} cleavagereported by Staples(1935) on crystals from Gold Hill, Utah, was not observed. Fracture un- even. Brittle. Hardness3+. G.:4.435 +0.005 (an average of measure- ments of 8 difierent crystals on the microbalance); 4.435 (calculated). The specific gravity found for the Mapimi adamite, which is essentially pure Zn2(AsOrOH) is comparable to the values 4.475 and 4.484 re- ported by de Schulten (1903) for the pure artificial compound and by Rosickf (1910) for pure adamite from Thasos, Turkey. Lower values, rangingbetween 4.319 and 4.35,have beenfound for material containing Cu, Co or Fe" in substitutionfor Zn. Luster vitreous. Small crystalson the specimensare nearly colorless,while the larger crystals are greenish- yellow; all are transparent. The Mapimi adamite fluoresces a bright lemon yellow with a pale lemon yellow phosphorescencein short-wave ultraviolet radiation; a much weaker reaction is given in long-wave ultra- violet and in r-rays (pale bluish-green). Specimensfrom other localities react variously. A blue-green Laurium specimen gave a weak greenish fluorescencein both long- and short-wave ultraviolet; bluish-green, in K-rays. Negative results were obtained with a colorlessspecimen from Laurium, a blue-greenspecimen from Gold Hill, Utah, cobaltian material from Cap Garonne, France, and Tsumeb, Africa, and with cuprian ma- terial from Tsumeb. 452 MARY E, MROSE, DAN E, MAYERS AND FRANCIS A. WISE -;j ?. aE.q1 ^ =Y - d MJ hF 2'* 95€ .3i*, * 'Ac=-.o^9^ --i -i -i ri 3 ;; +t +t +l \llo u =t Nh h **- 9 -- +r:9 o o o r/ /\ N € . .n \ 6€ +t +l +l J I ,Hj i --* X ^ N++ il f9<* 3 x -6- E s 888- 3* ???" HE ii A^ : s B f 3S g;E i :::l,i EE9* p : ooo rl 9 o o P 9= E {,3r:i H9lhr >9 * .'- lRFii5, s-vs.'x' F J -J-jxI 333.59 €€o fr F" 833- p E F A ooo il o o E ! +r+r+r N.: o u aq E]' ppsi I €qEIs u Jr.ix'.' E=9,9R F F ooo6:1 nnnr; o R$3 ? s -.; r' ..i x i e A -- .i.: o a -.Uo."9Eix>sE'E .9E F.X* CJ UlH dN ADAMITE FROM MAPIMI, MEXICO 453 Oprrcar Pnopnnrtps The optical properties of the Mapimi adamite are cited in Table 4 in comparison with those reported on material from other localities. The wide variation in the indices of refraction is due to variation in the chem- ical composition of the crystals, as is clearly shown by comparison of the data on the cuprian and cobaltian material from Tsumeb, but since chemical analyses are lacking in most instances the nature of the rela- tionship is not clear. X-Rav Srunv A selectedsingle-crystal of the Mapimi adamite was studied by the Weissenberg r-ray method. The unit cell dimensions, given in Table 5, are in close agreement with those obtained by Strunz (1936) and Kok- koros (1937) on adamite from Thasos and Laurium. The Weissenberg films exhibited orthorhombic centro-symmetry. If the crystal class is TAslo 5. UNrr Cnr,r Druoxsror.rsol Almrrrn 1 .t Adamite (Mapimi) Adamite (Thasos) Adamite (Laurium) (Mrose, 1948) (Strunz, 1936) (Kokkoros, 1937) &o 8.30+0.02 8.32 8.31 bo 8.51 + 0.02 8.54 851 Co 6.04+ 0.02 6.08 6.06 asibsics 0.975:1:0.706 0.974:l:0.712 0.977:lto 712 ao/co 1.38 1.37 1.37 Vo 427 431 429 Space group Pnnm Pnnm Pnnm taken to be dipyramidal, as is indicated by the form development (sum- marized by Ungemach (1921)) and by the absenceof piezoelectricity, the spacegroup is establishedby the diffraction effects as Pnnm in conform- ance with that earlier reported. The spacing data obtained from a powder photograph of the Mapimi material are listed in Table 6. Photographs of the adamite pattern and of the isostructural species olivenite, Cuz(AsOd(OH), and libethenite, Cuz(POa)(OH),are given by Richmond (1940).