Kampfite, a new barium silicate carbonate mineral species from Fresno County, California

Kampfite, ideally Ba-6[(Si,Al)O-2](8)(CO3)(2)Cl-2(CI,H2O)(2), is a newly id entified mineral species found in barium-silicate-rich deposits at Big Cree k and Rush Creek, Fresno County, California. It forms irregular masses up t o 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 phys ical properties are: brittle, translucent, nonfluorescent, vitreous luster, white streak, hardness 3, uneven fracture. Kampfite is uniaxial negative, omega 1.642(2), epsilon 1.594(2), nonpleochroic. It is hexagonal, with unit -cell parameters refined from powder data: a 5.244(2), c 29.83(1) Angstrom, V 710.5(4) Angstrom (3), and Z = 1. The strongest seven lines of the X-ray powder-diffraction pattern [d in Angstrom (I)(hkl)] are: 14.67(100)(002),3 .883(100)(104),3.357(50)(106), 2.988(60)(00 (1) over bar(0) over bar), 2.88 7(50)(108),2.616(70)(110), and 1.969(50)(11 (1) over bar(0) over bar). Prec ession photographs show that possible space-groups are P6(3)/mmc, P (6) ove r bar 2c, P6(3)mc, P (3) over bar (1)c and P3(1)c. The empirical formula of kampfite (based on the average of three electron-microprobe analyses, norm alized on 26 anions) is: (Ba5.83Na0.04Ca0.02)Sigma (5.89) [(Si5.18Al2.36)(S igma7.54)O-15.08](CO3)(2)Cl-2[(H2O)Cl-0.45]Sigma1.45. The calculated densit y is 3.51 g/cm(3). All crystals studied contain inclusions or are multiple. Thus, it was not possible to unambiguously determine the correct space-gro up or precise details of the structure. However, the preliminary results sh ow that the structure is based on double layers of tetrahedra, [T4O8](infin ity), consisting of six-membered rings, with three layers of Ba polyhedra c onnecting 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, Lo s Angeles County Museum of Natural History, for his many significant contri butions to the study of new and rare minerals.