Botelho et al.,1994

Yanomamite, In(AsO4)2H2O, a new indium mineral from topaz-bearing greisen in the Goiás Tin Province, Brazil

Botelho,N.F.
Roger,G.
D'Yvoire,F.
Möelo,Y.
Volfinger,M.

European Journal of Mineralogy(1994), 6: 245-254.

Palavras chave: Arsenato, Granito, Greisen, Indio, Sulfeto

Abstract

Yanomamite occurs as green to yellow-green 0.2 mm dipyramidal crystals in aggregates associated with scorodite in quartz-topaz greisen in the tin deposit of Mangabeira, Goiás State, Brazil. Yanomamite crystals are always coated by a film of In-rich scorodite. Electron microprobe analysis gave In₂0₃ 45.80, Fe₂0₃ 1.11, Al₂0₃ 0.21, As₂0₅0.10, H₂0 (by difference) 12.78, sum 100 wt%, corresponding to (In_O.94Fe_0.04Al_0.01) As04.2.02H₂0. Yanomamite is isotypic with scorodite, and belongs to the variscite series. The mineral has vitreous luster, white streak, VHN₂₅= 631 (571-743) kg/mm², and is soluble in strong HCl or H₂S0₄. Dcalc = 3.876(3) glcm³ for Z = 8. Yanomamite is colorless in transmitted light, biaxial positive, and has 2 V = 55-76°, average n = 1.65, orientation X = a, Y = c, Z = b. Single-crystal X-ray study indicated orthorhombic symmetry, space group Pbca, a = 10.446(6), b = 9.085(4), c = 10.345(6) A as refined from the powder pattern; strongest lines (CoKal radiation) are 5.70(70, 111), 4.53(100,020,210), 4.163(50,021), 3.874(60,121), 3.250(60,122), and 3.110(50,311), in good agreement with data for synthetic InAs0₄.2H₂0.
The Mangabeira tin deposit contains several In-bearing minerals, including sphalerite with up to 11 wt% In. The maximum In content found in scorodite overgrowths is 6 wt% In₂0₃, corresponding to Fe_O.90In_0.l0; maximum Fe substitution in yanomamite is In_0.85Fe_0.l5, suggesting a possible miscibility gap. The origin of yanomamite is thought to be related to a hydrothermal event rather than later oxidation, formed by alteration of early arsenopyrite and In-rich sphalerite. The new name relates to the Yanomami Indians of the Amazon. Type material is in the museum of the Ecole Nationale Superieure des Mines de Paris, France, and in the Mineralogical Collection of the Instituto de Geociencias, Universidade de Brasília, Brazil.