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

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, 1.642(2), 1.594(2), nonpleochroic. It is hexagonal, with unit-cell parameters refined from powder data: a 5.244(2), c 29.83(1) Å, V 710.5(4) Å3, and Z = 1. The strongest seven lines of the X-ray powder-diffraction pattern [d in Å(I)(hkl)] are: 14.67(100)(002), 3.883(100)(104), 3.357(50)(106), 2.988(60)(00¯1¯0), 2.887(50)(108), 2.616(70)(110), and 1.969(50)(11¯1¯0). Pre-cession photographs show that possible space-groups are P63/mmc, P¯62c, P63mc, P¯31c and P31c. 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, [T4O8], consisting of six