KAMPFITE, A NEW BARIUM SILICATE CARBONATE MINERAL SPECIES FROM FRESNO COUNTY, CALIFORNIA

Abstract

Kampfite, ideally Ba6[(Si,Al)O2]8(CO3)2Cl2(Cl,H2O)2, is a newly identified mineral species found in barium-silicate-rich deposits at Big Creek and Rush Creek, Fresno County, California. It forms irregular masses up to 10 mm in size enclosed in quartz-rich portions of the sanbornite-bearing rock. It is light blue-grey, with one perfect cleavage on {001}. Other physical properties are: brittle, translucent, nonfluorescent, vitreous luster, white streak, hardness 3, uneven fracture. Kampfite is uniaxial negative, ω 1.642(2), e 1.594(2), nonpleochroic. It is hexagonal, with unit-cell parameters refined from powder data: a 5.244(2), c 29.83(1) A, V 710.5(4) A3, and Z = 1. The strongest seven lines of the X-ray powder-diffraction pattern [ d in A( I )( hkl )] are: 14.67(100)(002), 3.883(100)(104), 3.357(50)(106), 2.988(60)(0010), 2.887(50)(108), 2.616(70)(110), and 1.969(50)(1110). Precession photographs show that possible space-groups are P 63/ mmc , P 62 c , P 63 mc , P 31 c and P 31 c . The empirical formula of kampfite (based on the average of three electron-microprobe analyses, normalized on 26 anions) is: (Ba5.83Na0.04Ca0.02)∑5.89[(Si5.18Al2.36)∑7.54O15.08](CO3)2Cl2[(H2O)Cl0.45]∑1.45. The calculated density is 3.51 g/cm3. All crystals studied contain inclusions or are multiple. Thus, it was not possible to unambiguously determine the correct space-group or precise details of the structure. However, the preliminary results show that the structure is based on double layers of tetrahedra, [ T 4O8]∞, consisting of six-membered rings, with three layers of Ba polyhedra connecting the layers of tetrahedra. Kampfite is part of the monteregianite-(Y) – wickenburgite series (Strunz classification) and is structurally and chemically similar to cymrite. The mineral name honors Anthony R. Kampf, Los Angeles County Museum of Natural History, for his many significant contributions to the study of new and rare minerals.