Yanomamite, InAsO (sub 4) .2H (sub 2) O, a new indium mineral from topaz-bearing greisen in the Goias tin province, Brazil

Yanomamite occurs as green to green-yellow idiomorphic crystals in aggregates associated with scorodite in quartz-topaz greisen in the Mangabeira Sn deposit, Goias State; the crystals are always coated by a thin film of In-rich scorodite. EPMA gave In (sub 2) O (sub 3) 45.8, Fe (sub 2) O (sub 3) 1.1, Al (sub 2) O (sub 3) 0.21, As (sub 2) O (sub 5) 40.1, H (sub 2) O (by difference) 12.78, leading to the formula (In (sub 0.94) Fe (sub 0.04) Al (sub 0.01) )AsO (sub 4) bullet 2H (sub 2) O. Indexed XRD powder data are tabulated; strongest lines 4.53(100), 5.70(70), 3.874(60), 3.250(60), 4.163(50), 3.110(50) Angstrom ; a 10.446, b 9.085, c 10.345 Angstrom ; space group Pbca, Z = 8 (the Fe-free synthetic compound has a slightly larger unit cell). Yanomamite has average refr. ind. 1.65, 2V (sub gamma) 55-76 degrees, D (sub calc.) 3.876 g/cm (super 3) , VHN (sub 25) 631 kg/mm (super 2) . It is isotypic with scorodite, and belongs to the variscite series. Yanomamite and In- bearing scorodite are cogenetic, and formed by alteration of early arsenopyrite and In-rich sphalerite; this replacement may be related to a hydrothermal process coeval with the main cassiterite deposition, rather from the supergene alteration. The name is after the Yanomami Indian people from Amazon.