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Formula: PtCu
Alloy
Crystal System: Trigonal
Specific gravity: 15.71 measured, 15.63 calculated
Hardness: 4
Streak: Black
Colour: Grey, lead-grey, steel-grey, may be tarnished brown
Solubility: Insoluble in hydrochloric and nitric acid
Environments
Occurrence:
Localities
At Itabira, Minas Gerais, Brazil, hongshiite occurs associated with
palladian gold, and more rarely with
native platinum, in the sulphide-free,
hematite-rich itabirite
mineralisation. Hongshiite occurs in grains up to about 1.5 mm in cross-section. The crystals (>0.1 mm) are
generally covered by a porous rim from which copper is preferentially leached,
eventually forming a rind of nearly pure native platinum. Submicrometre-sized
crystals, acicular in shape, replace an octahedral precursor phase, interpreted to be
magnetite. The magnetite could
have acted as a local redox barrier to the passage of oxidising hydrothermal fluids leading to hongshiite
precipitation. Sperrylite,
isomertieite, atheneite,
sudovikovite and baryte occur as
euhedral to anhedral inclusions in the larger crystals of hongshiite; patches of
platinum-bearing
tetra-auricupride occur within hongshiite
CM 40.711-723.
At the type locality, Hongshila Pt-Pd deposit, Boluonuo, Fengning county, Chengde, Hebei, China, hongshiite
occurs in an actinolised
diopside-type of platinum deposit,
and in Alpine-type ultramafic intrusives and related placers. It is
lead-grey with metallic lustre and a black streak.
Associated mineras include cooperite,
sperrylite, vysotskite,
isomertieite, magnetite,
bornite, polydymite,
diopside, actinolite,
isoferroplatinum,
fengluanite and epidote
(AM 69.411-412, HOM, Mindat).
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