gsminmag Mineralogical Magazine Mineralogical Magazine 0026-461X Mineralogical Society 10.1180/minmag.1978.042.322.02 Bahianite, Sb3A15O14(OH)2, a New Species Moore Paul B. Department of the Geophysical Sciences, The University of Chicago, Chicago, Illinois 60637, U.S.A. Barbosa Carlos do Prado Praca N.S. da Glorida 135-207, Rio de Janeiro 20000, Brazil Gaines Richard V. Hoffecker Road, Pottstown, Pennsylvania 19464, U.S.A. 6 1978 42 322 179 182 20 7 1977 Copyright © 1978, The Mineralogical Society 1978 Summary

Bahianite, Sb3Al5O14(OH)2-Sb3Al5(Al, Be, Si)<2016, monoclinic, a 9·406(6), b11·541(8), c 4·410(3) Å, β 90·94(3)°, Z = 2, space group C2/m, is a new species from the Paramirim region, south central Bahia state, Brazil. It occurs as water-worn pebbles (‘favas’) with quartz, andalusite, kyanite, diaspore, eskolaite, cassiterite, etc. Colour tan to cream, crystals in vugs colourless, tan or pale violet. Specific gravity ranges from 4·89 to 5·46 (5·26 g cm−3 for Sb3Al5O14(OH)2); hardness 9, cleavage (100) perfect, lustre adamantine, biaxial (−), 2V large, perfect, lustre adamantine, biaxial (−), 2V large, α = 1·81, β = 1·87, γ = 1·92, dispersion r > v.

The crystal structure represents a new type and is based on hexagonal close-packed oxygens. It is related to the structure of simpsonite Ta3Al14O13(OH).