Abstract

Franciscanite and 6rebroite are new mineral species isotypic with welinite.

Franciscanite, ideally Mn6[V,□]2Si2(0,0H)~l4, is hexagonal, has space group P3, with a = 8.148(1) and c = 4.804(1) Å, V= 276.2 Å3, Z = 1. It is dark brownish red, with vitreous luster, and no cleavage; Dmeas = 4.1 and Dcalc = 3.93 g/cm3. It is found with sonolite, hausmannite, and gageite in the Franciscan Complex at the Pennsylvania mine in the San Antonio Valley, Santa Clara County, California.

Örebroite, ideally Mn6[Sb5+,Fe3+]2Si2(0,0H)~l4, is hexagonal, has space group P3, with a = 8.183(7) and c = 4.756(9) Å, V = 275.8 Å3, Z = 1. It is dark brown with vitreous luster and no cleavage; Dcalc = 4.77 g/cm3. It is found associated with calcite at the Sjö mine, Örebro, Sweden.

New data for welinite indicate the revised formula Mn6[W,Mg]2Si2(0,0H)~l4 and space group P3. Gageite, associated with franciscanite, has the composition Mn38 84-Mg0.58Fe0.16Si15(0,0H)90, supporting the occurrence of octahedral vacancies in gageite and balangeroite.

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