Hagstromite, Pb8Cu2+(Te6+O6)2(CO3)Cl4, a new lead–tellurium oxysalt mineral from Otto Mountain, California.

Anthony R. Kampf1,, Robert M. Housley2, Stuart J. Mills3, George R. Rossman2 and Joe Marty4

 
1Mineral Sciences Department, Natural History Museum of Los Angeles County, 900 Exposition Blvd., Los Angeles, CA 90007, U.S.A.
2Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, U.S.A.
3Geosciences, Museums Victoria, GPO Box 666, Melbourne 3001, Victoria, Australia

45199 E. Silver Oak Road, Salt Lake City, UT 84108, U.S.A


ABSTRACT

Hagstromite, Pb8Cu2+(Te6+O6)2(CO3)Cl4, is a new tellurate mineral from Otto Mountain near Baker, California, U.S.A. It occurs on quartz in association with cerussite, fuettererite and thorneite. It is a secondary oxidation zone mineral and is presumed to have formed by oxidation of earlier formed tellurides, chalcopyrite and galena. Hagstromite occurs as light yellow–green blades, up to about 100 Ám long. Crystals are transparent with adamantine to silky luster. The mineral is brittle with two cleavages providing splintery fracture; the Mohs hardness is probably between 2 and 3. The calculated density is 7.062 g cm–3. Hagstromite is optically biaxial (+), with calculated indices of refraction α = 2.045, β = 2.066), γ = 2.102; 2Vmeas = 76(1)░; optical orientation X = b, Y = a, Z = c. The Raman spectrum of hagstromite exhibits similarities with those of agaite and thorneite and confirms the presence of CO32. The electron microprobe analyses provided the empirical formula Pb8.07Cu2+0.98Te6+1.96C1.17Cl3.83O15.34. Hagstromite is orthorhombic, space group Ibam, with a = 23.688(17), b = 9.026(8), c = 10.461(8) ┼, V = 2237(3) 3 and Z = 4. The crystal structure of hagstromite (R1 = 0.0659 for 284 I > 2sI reflections) contains a novel Cu2+Te6+2O12 chain assembled of corner–sharing Cu2+O4 squares and Te6+O6 octahedra. The O atoms in the chains form bonds with Pb2+ cations, which in turn bond to Cl and CO32– anions, thereby creating a framework structure.

Hagstromite
Hagstromite crystals (photo credit: AR Kamph)