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Formula: Ir
Native element, transition metal
Osmiridium is a variety of iridium rich in osmium, but still
isometric.
Ruthenosmiridium is a variety of iridium rich in ruthenium
and osmium.
Crystal System: Isometric
Specific gravity: 22.65 to 22.84 measured, 22.66 calculated
Hardness: 6 to 7
Streak: White
Colour: Silver-white
Solubility: Resists attack by any acid
Melting point: 2447oC
Boiling point: 4430oC
Abundance in the Earth’s crust: 0.4 parts per billion by mass, 0.05 parts per billion by moles
Abundance in the Solar System: 2 parts per billion by mass, 0.01 parts per billion by moles
Common impurities: Os,Ru,Pt,Au,Pd,Cu,Fe
Environments
Plutonic igneous environments
Placers
Iridium occurs in platinum-bearing ultra-basic rocks and in placers
derived from them, always alloyed with other platinum group elements (Dana).
Associated minerals include platinum and
platinum-iron alloys
(HOM).
Abnormally high amounts of iridium have been found in rocks dating to the boundary between the Cretaceous and
Tertiary periods (65 million years ago). This has led to a widely held view that an
iridium-containing comet struck the Earth at that time, leading to the extinction of the dinosaurs and many other
forms of life
(ChC).
Iridium-bearing minerals include:
Alloys
rutheniridosmine
Antimonides - the antimonide anion is Sb3-
fleetite
Sulphides - the sulphide anion is S2-
cuproiridsite
ferhodsite
irarsite
iridarsenite
kashinite
kingstonite
kuvaevite
malanite
tamuraite
tolovkite
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