Mineralogical Magazine Volume 43 Number 328 December 1979
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MINERALOGICAL MAGAZINE VOLUME 43 NUMBER 328 DECEMBER 1979 Girdite, oboyerite, fairbankite, and winstanleyite, four new tellurium minerals from Tombstone, Arizona S. A. WILLIAMS Phelps Dodge Corporation, Douglas, Arizona SUMMARY. Girdite, HzPb3(Te03)Te06 is white, H.= 2, species have been identified: hessite, empressite, D = 5.5. Crystals are complexly twinned and appear krennerite, rickardite, and tellurium. Altaite has monoclinic domatic. The X-ray cell is a = 6.24IA, b = not been found although relict galena is not 5.686, c = 8.719, /3 = 91°41'; Z = I. uncommon. Oboyerite is H6Pb6(Te03h(Te06Jz' 2HzO. H = 1.5, Girdite. About a dozen samples displaying this D = 6.4. Crystals appear to be triclinic but are too small for X-ray work. mineral were found. Girdite usually occurs as Fairbankite PbTe03 is triclinic a 7.8IA, b 7-JI, spherules up to 3 mm in diameter. These are dense, ()( = = c 6.96, 117°12', /3 4. chalky, and brittle with little hint of a crystalline = ()(= = 93°47", Y = 93°24', Z = Indices are = 2.29, /3 = 2.31, Y = 2.33. druse on the surface. The spherules resemble those Winstanleyite, TiTe30s, is cubic fa3, a = 10.963A. of oboyerite closely, they also resemble warty crusts Crystals are cubes, sometimes modified by the octa- of kaolin and hydronium alunite to be found at the hedron; colour Chinese yellow, H = 4, no = 2.34. locality. The first specimen found, however, was All of the above species were found in small amounts on exceptional. This has spherules and bow-tie aggre- the waste dumps of the Grand Central mine, Tombstone, gates of slender tapered prisms; these spherules are Arizona, associated with a wealth of other tellurites and tellurates. up to 6 mm across. The tapered prisms are seen in thin section to be polycrystalline and at their terminations there may be clear, complexly twinned crystals that seem to be monoclinic with SINCE the discovery of rodalquilarite at Tomb- class m symmetry. stone, Arizona, more than thirty new tellurium Girdite spherules usually occur on fracture oxysalts have been found there. The use of a back- surfaces within sheared vein quartz gangue or hoe to excavate in the remains of waste dump cutting a massive wallrock composed mostly of material facilitated the discovery of eighteen new adularia. Species occurring within these ores (and species at the Grand Central mine alone, and it was presumably paragenetically older) include rodal- during this project that these four new species were quilarite, chlorargyrite, gold, anglesite, and found. unknown tellurites or tellurates. Still other un- Tellurium minerals were noted by Rasor (1937) in known species occur on fractures with girdite. the Joe Shaft, a companion to the Grand Central, Although spherules are tough and brittle the but were not investigated. Evidently they were once Mohs hardness is only 2. The specific gravity, deter- abundant, for emmonsite and rodalquilarite are mined by Berman Balance in toluene on a sample of fairly common in the waste dumps. All other 3.8 mg is 5.5::!::0.2 (avg. of three trials). Girdite is tellurium minerals are rare however, and they seem non-fluorescent. to have occurred only in the richest ores. Spectrographic analysis of girdite showed only Little is known of the primary ores whose oxida- Pb, Te, and Ag (the latter due to microscopic inclu- tion produced such a wealth of tellurites and sions of chlorargyrite) and microchemical methods tellurates. At the Grand Central mine the following failed to detect any other anions. Wet chemical i!J Copyright the Mineralogical Society 454 S. A. WILLIAMS T ABLE I. Chemical analyses of girdite excavations in the waste dumps of the Grand Cen- tral mine at Tombstone. Only two fist-sized pieces were found. The first of these is also the only known 2 3 4 5 specimen containing fairbankite and the study of both oboyerite and fairbankite was based entirely PbO 61.4 % 60.7% 6}.2 % 0.283 65-4% on this specimen. Te02 16.6 15.3 16.5 0.103 15.6 Te03 18.3 16.9 18.2 0.104 17.2 H2O (2.0) (2.0) 2.1 0.115 1.8 TABLE II. X-ray powder data for girdite. Insol. 0.7 2.5 Cr-KIX radiation, 114 mm camera 99.0 97-4 100.00 100.0 I d d I d est meas calc hkl est meas I. On 1620 Ilg 5.027 101 7 1.682 2. On 2242 Ilg 5.°°4 . 3.118 },119 200 1.670 }, A vg. of I and 2 reset to 100 % 7 7 10 3.°54 3.°55 1I2 2 1-562 4. Ratios 7 2.994 2.995 112 6 1.529 5. Theory for H2Pb3(Te03)Te06 8 2.842 2.843 020 4 1.499 1/2 2.71 I 2.7°3 021 3 1.424 1/2 2.516 2.5°2 202 6 1.383 analyses of two samples are presented in Table I. In 1/2 2.39° 2.381 022 7 1.368 2.179 2.179 1.343 each analysis, some quartz and chlorargyrite were 5 °°4 5 recovered and weighed as 'insol.' but in dealing with 7 2.102 2.101 220 5 I. 328 such tiny amounts losses of even traces of material I 1.967 1.966 213 6 1.295 1.814 3 1.288 could easily explain the low analytical summations. 5 1.813 { [3° 1.8I I 3 1.253 Girdite is readily soluble in cold I: I HN03 and 2°4 5 1.802 1.801 312 5 I.I93 HCl. Water was determined quantitatively in the I.762 204 I.I84 8 I.765 { 7 closed tube (and easily seen) using a 3.777 mg I.764 312 4 I.I74 sample. Loss of water occurred during decrepita- 5 I.73 I 1.729 024 4 I.I67 tion, followed by fusion to a blebby-yellow slag. I.726 214 4 I.I 53 Although no single crystals were found, a few fragments were obtained from the tips of the bow- tie 'crystals' described earlier. Even the best frag- The rock consists mainly of fine-grained adularia ments obtained showed only a few crystal faces and (altered shale) hosting fine-grained jarosite pseudo- were too small to orient for optical goniometry. morphs after pyrite and squarish, partly filled or One such fragment was employed for rotation and lined voids derived from galena. These voids are Weissenberg level photographs giving the follow- typically lined with jarosite and fairbankite crys- ing cell: a = 6.241A, b = 5.686, c = 8.719, f3= tals, then coated with clear, botryoidal opal. 91°41'. With Z = I, the calculated density is Perched on the opal are tiny milk-white spherules 5-49 gjcm3 (using the ideal formula for the calcula- of fibrous oboyerite. Later veins cut the rock carry- tion). Powder data were used to refine the cell and ing rodalquilarite, cerussite, and an unknown are presented in Table II. tellurium mineral. The crystal fragments gave the following optic The spherules have an estimated Mohs hardness orientation: y = b, f3:[001] 34° (in acute 13).The of 1.5, readily breaking down into individual fibres indices were measured in S-Se melts as IX= 2-44, no more than 60 ,um in length. No fluorescence was 13= 2-47, Y= 2-48. The 2Vd measured is 70° and observed. The specific gravity was estimated as 6.4 strong dispersion p > v can be seen in larger using 213 ,ug for Thoulet's method, but the preci- crystals. The petrographer probably could not sion on this tiny sample was i:o.6. identify the typically fine-grained material in thin Spectrographic analysis showed major Pb, Te, section for it resembles any number of lead Ca, and Ag (the latter as traces of included AgCl). minerals; coarser crystals could eaf.ily be mistaken Wet chemical analysis on a sample of 970 ,ugpro- for fairbankite. vided the results in Table III. 16 ,ug of quartz and The mineral is named to honour Richard Gird, chlorargyrite were recovered and weighed as insol. mining engineer and assayer, who assayed the first Water was determined on another sample of rich silver ores found at Tombstone and, with the 1.010 mg by the Penfield method. Schicffelin brothers, worked to open up the district. Oboyerite is readily soluble in cold, dilute HN03 Oboyerite. This new species was found during and slowly soluble in 16% HCI. Fusion to a NEW TELLURIUM MINERALS FROM ARIZONA 455 T ABLE II I. Chemical analysis of oboyerite cleavage. Viewed normal to the cleavage, one set of striae can be faintly seen at an angle of 63° to the length of the crystal, or the crystal may be truncated 2 3 at this angle. The partial birefringence in this PbO 58.0% 0.260 58.6% orientation is 0.002 with no observable dispersion. CaO 0.3 0.053 0.3 If a fibre is rotated on its length and viewed normal Te02 22.1 0.138 21.4 to the rotation axis, the maximum extinction angle TeO, 16.2 0.092 15.7 of 37° occurs somewhere between the positions H2O 4.2 0.238 4.0 where the cleavage is normal and parallel to the direction of view. This fact demonstrates that the 100.8 100.0 crystals are triclinic. The minimum and maximum indices were deter- I. By wet analysis on 954 /lg (after correcting for 16 /lg mined in S-Se melts: rJ. of insol.) = 2.24, Y = 2.26.