Formula: Mg6Fe3+2(OH)16Cl2.4H2O
Hydroxide, hydrotalcite group
Specific gravity: 2.11
Hardness: 1½
Streak: White
Colour: Bluish green, becoming pale green with a rusty red tint on exposure to air (alteration to pyroaurite)
Solubility: Insoluble in water, readily soluble in mineral acids
Environments
Carbonatites
Metamorphic environments
Iowaite occurs in veinlets in serpentinite as an alteration
product of serpentine
(HOM, Webmin).
Localities
At the type locality, Matlock drill core, Sioux county, Iowa, USA, iowaite occurs in veinlets in
serpentinized olivine-rich
ultramafic rocks. Associated minerals include
chrysotile, dolomite,
brucite, calcite,
magnesite, pyroaurite and
pyrite. It appears that the introduction of the vein material postdates the
serpentinisation of the rock
(AM 52.1261-1271, R&M 93.3.271-273).
At the Komsomol'skii Mine, Talnakh Cu-Ni Deposit, Noril'sk, Putoran Plateau, Taimyr Peninsula, Taymyrskiy Autonomous Okrug,
Krasnoyarsk Krai, Russia, iowaite occurs as crystals to 2.5 cm with valleriite,
szaibélyite, magnetite,
brucite and serpentine in
metamorphosed dolostone associated with
porphyry copper deposits
(Dana).
At the Palabora mine, Loolekop, Phalaborwa, Limpopo, South Africa, iowaite is a late-generation mineral, found in
cavities in carbonatite in the lowest level of the Palabora open pit. The carbonatite here consists mainly of
calcite and dolomite with much
magnetite, and also biotite,
phlogopite, and chondrodite.
Cavity minerals associated with the iowaite include magnetite,
chondrodite, clinochlore and
smaller amounts of brucite,
hydrotalcite, phlogopite,
fluoborite, fluorite,
apatite, baryte,
celestine, antigorite,
calcite and dolomite. On a few specimens,
iowaite is overlain thinly by calcite. Many crystals contain inclusions of
magnetite
(R&M 92.5.441-442, HOM).
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