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Formula: RuAs2
Arsenide of ruthenium,
lollingite group, forms a series with
omeiite
Crystal System: Orthorhombic
Specific gravity: 8.692 calculated
Hardness: 6½ to 7
Streak: Greyish black
Colour: Lead-grey
Solubility: Insoluble in 1:1 nitric acid and hydrochloric acid
Common impurities: Ir,Cu,Sb,S
Environments
Anduoite is of magmatic origin, as very rare inclusions in
chromium-rich spinel in
chromitite bodies enclosed variously by
augite peridotite,
serpentinised
dunite, harzburgite
and pyroxenite. Associated minerals include
chromium-rich spinel,
pyrite, pyrrhotite,
marcasite, magnetite,
chalcopyrite, molybdenite,
galena, millerite and
violarite
(HOM).
Localities
The Maja e Sukës deposit, Has, Kukës County, Albania, occurs in a body of
serpentinised
dunite. Disseminated ore is prevalent at the rim of the
chromite deposit, in the contact zone with the host
dunite.
In a sample of platinum-rich
chromitite, a grain of anduoite was found included in a
grain of chromium-rich spinel. The
assemblage is composed of sperrylite, which forms a wide discontinuous
rim around platinum group minerals of finer grain-size, filling the
space between these platinum group minerals and the host
chromium-rich spinel.
Anduoite (3 microns in diameter) occurs in the fine-grained
platinum group minerals assemblage with
hollingworthite, which is intergrown with a complexly zoned
sulfarsenide of rhodium,
iridium, palladium and
nickel
(CM 39.591-606).
At the type locality, the Anduo Cr deposit, Amdo county, Nagchu Prefecture, Tibet, China, anduoite occurs as
massive grains or granular aggregates (60 to 100 microns in size) in a
chromium deposit related to augite
peridotite and dunite.
The host rock is an altered dunite. The main ore mineral is
chromium-rich spinel with minor
pyrite, pyrrhotite,
marcasite, magnetite,
chalcopyrite, molybdenite,
galena, millerite and
violarite. Other
platinum group minerals present are
ruthenarsenite,
sperrylite, ruthenium-rich
iridarsenite, irarsite,
osarsite, osmiridium,
ruthenosmiridium,
laurite and ruarsite.
Anduoite and other arsenides and
sulpharsenides, often distributed around the grains of
rutheniridosmine, are closely associated with
irarsite and show replacement of
irarsite.
Anduoite has also been found in placers near the host rock body with
iridosmine, osmiridium,
osmium, an
iron-ruthenium mineral, and minor
sperrylite, osarsite,
ruarsite, iridarsenite, and
irarsite
(AM 65.808-809).
The Kapitanov Cr deposit, Zvenyhorodka Raion, Cherkasy Oblast, Ukraine, includes lenses and veins of massive and
disseminated varieties of chromite ores hosted by
serpentinised and carbonatised
dunite, harzburgite
and, rarely, by pyroxenite. Grains of
chromium-rich spinel are of
variable size and composition. Other minerals observed are ilmenite,
magnetite, serpentine,
forsterite, orthopyroxene and
clinopyroxene. Opaque minerals in the
serpentine matrix and in some cases within the grains of
chromium-rich spinel include
millerite, nickeline,
gersdorffite, maucherite,
pentlandite, violarite,
arsenic-bearing tučekite,
chalcopyrite and galena. The
ores also carry platinum group minerals including anduoite,
irarsite, laurite,
ruarsite and minor sperrylite.
Two inclusions of anduoite were observed in massive
chromitites. One is a 6 to 9 micron euhedral crystal enclosed in a
grain of chromium-rich spinel that
is free of fractures and contains numerous lamellae (10 to 12 microns long and 0.5 to 1 micron wide) of
ilmenite. Another crystal of anduoite is small (1 to 2 microns) and
euhedral; it occurs in a grain of chromium-rich
spinel that is also free of cracks or other inclusions
(CM 39.591-606).
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