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Published August 2010 | public
Journal Article

Lead-tellurium oxysalts from Otto Mountain near Baker, California: I. Ottoite, Pb_2TeO_5, a new mineral with chains of tellurate octahedra

Abstract

Ottoite, Pb_2TeO_5, is a new tellurate from Otto Mountain near Baker, California. Most of the mining on Otto Mountain occurred between 1940 and 1970 and is attributed to Otto Fuetterer, for whom the mountain is now named. The new mineral occurs on fracture surfaces and in small vugs in brecciated quartz veins, which intersect granitic rocks. Ottoite is directly associated with acanthite, bromine-rich chlorargyrite, gold, iodargyrite, khinite, wulfenite, and four other new tellurates: housleyite, markcooperite, thorneite, and timroseite. Various other secondary minerals occur in the veins, including two other new secondary tellurium minerals, paratimroseite and telluroperite. Ottoite and most other secondary minerals of the quartz veins are interpreted as having formed from the partial oxidation of primary sulfides and tellurides during or following brecciation of the veins. A later generation of quartz mineralization then recemented the breccias, effectively isolating and protecting the secondary mineralization from further alteration. Ottoite is monoclinic, space group I2/a, with the unit cell: a = 7.5353(6), b = 5.7142(5), c = 10.8981(12) Å, β = 91.330(6)°, V = 469.13(8) Å^3, and Z = 4. The mineral occurs as complex spear-shaped crystals in subparallel to divergent intergrowths. It is yellow and transparent to translucent, with a pale yellow streak and adamantine luster. Mohs hardness is estimated at 3. The mineral is brittle, with an irregular fracture and two cleavages in the [100] zone at ~90°—possibly on {010} and {001}. The calculated density is 8.721 g/cm^3. Ottoite is biaxial (–), with a large 2V, but indices of refraction are too high to be measured. The optic orientation could only partially be determined: Y ≈ a. No pleochroism was observed. Electron microprobe analyses provided the following averages: PbO 68.88 and TeO_3 28.03, total 96.95 wt%; the empirical formula (based on O = 5) is Pb_(1.96)Te_(1.01)^(6+)O_5. The strongest powder X-ray diffraction lines are [d_(obs) in Å (hkl) I]: 3.131 (202) 64, 3.055 (013) 90, 3.015 (211) 100, 2.112 (222) 29, 1.810 (006, 215) 21, 1.773 (411, 402) 43, 1.686 (033, 231) 20. The crystal structure (R_1 = 0.020) consists of straight chains of trans-corner-sharing Te^(6+)O_6 octahedra parallel to a, which are joined by bonds to Pb atoms. The Pb atom exhibit markedly lopsided 11-coordination, typical of Pb^(2+) with stereoactive 6s^2 lone-pair electrons. The powder X-ray diffraction pattern of ottoite is very similar to that reported for girdite. Examination of girdite type material suggests that its description was based upon data obtained from at least two and possibly three different phases, one of which may correspond to ottoite.

Additional Information

© 2010 Mineralogical Society of America. Manuscript received January 27, 2010. Manuscript accepted April 12, 2010. Manuscript handled by G. Diego Gatta. Pier F. Zanazzi, an anonymous reviewer, Technical Editor Ronald C. Peterson, and Associate Editor G. Diego Gatta are thanked for helpful comments on the manuscript and especially for suggestions regarding the crystal-structure refinement. Michael Rumsey is thanked for making available fragments from the type specimen of girdite in The Natural History Museum, London. Richard Thomssen is thanked for the loan of another specimen of girdite. The microprobe analyses were supported by a grant to the California Institute of Technology from the Northern California Mineralogical Association. The remainder of this study was funded by the John Jago Trelawney Endowment to the Mineral Sciences Department of the Natural History Museum of Los Angeles County.

Additional details

Created:
August 22, 2023
Modified:
October 20, 2023