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Formula: Mg6Cr2(OH)16Cl2.4H2O
Hydroxide, hydrotalcite group,
hydrotalcite supergroup,
chromium-bearing mineral
Crystal System: Trigonal
Specific gravity: 2.062 measured, 2.023 g/cm3 (Calculated)calculated
Hardness: 1&~189; to 2
Streak: Pale pink to white
Colour: Purple to deep magenta
Environments
Localities
At the type locality, the Mount Keith Open Pit, Mount Keith, Wiluna Shire, Western Australia,
woodallite is a new (in 2020) chromium-rich member of the
hydrotalcite group from the large, low-grade Mount Keith
nickel deposit. Woodallite occurs as whorls and clusters of minute
platelets up to 6 mm across in lizardite +
brucite altered dunite.
Individual platelets are typically 10–100 μm in maximum dimension and are often curved. Associated minerals include
chromite, lizardite,
iowaite, pentlandite,
magnetite, tochilinite and
brucite.
Woodallite forms as a result of hydrothermal alteration of
primary magmatic
chromite by chlorine-rich solutions at temperatures less than 320°C.
Relict chromite fragments are frequently present in the whorls, and
associated magnetite is altered extensively to
iowaite
(MM 65.427-436).
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