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Formula: In(AsO4).2H2O
Hydrated normal arsenate,
variscite group, forms a partial series with
scorodite,
indium-bearing mineral
Crystal System: Orthorhombite
Specific gravity: 3.876 calculated
Hardness: 3 to 4
Streak: White
Colour: Pale green to yellow green to greenish-yellow, not white
Common impurities: Fe,Al
Environments
Metamorphic environments
Hydrothermal environments
Yanomamite is a rare secondary mineral replacing
arsenopyrite in
quartz-topaz
greisen veins in granite
(HOM).
Localities
The type locality is the Mangabeira deposit, Monte Alegre de Goiás, Goiás, Brazil. This tin
deposit is associated with a granite intrusion. Yanomamite and other
indium minerals are hosted in
quartz-topaz
greisen veins associated with
lithium-mica/topaz/albite
granite. Three hydrothermal stages are inferred. The first stage minerals
include topaz, quartz,
zinnwaldite, wolframite,
löllingite, arsenopyrite with
indium-rich sphalerite inclusions and
minor cassiterite. The second stage is mainly represented by
cassiterite ore, and probably indium-rich
arsenates. Minerals from the third stage include
arsenopyrite, indium-poor
sphalerite, indium-bearing
stannite, roquesite,
chalcopyrite, pyrite,
enargite, galena,
digenite and cosalite. Minerals from
the youngest association, probably of supergene origin, are
indium-poor scorodite,
beudantite, agardite-(Y),
arsenates, goethite,
dzhalindite, covellite and
chalcocite.
In the type material, yanomamite occurs in an arsenopyrite alteration
zone, as euhedral grains to 0.2 mm in size, intimately intergrown with scorodite,
forming aggregates up to 1 cm across. Yanomamite also fills micro fractures and interstices in
gangue minerals, quartz and
topaz as well as lithium-mica cleavages.
Yanomamite crystals are often coated by a thin film of epitactic indium-rich
scorodite. It occurs in close association with
cassiterite in the arsenopyrite
alteration zone, but there is no cassiterite concentration in alteration
zones where yanomamite is absent
(EJM 6.245-254).
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