Formula: Mg6Fe3+2(OH)16Cl2.4H2O
Hydroxide, hydrotalcite group, hydrotalcite supergroup
Crystal System: Trigonal
Specific gravity: 2.11 measured
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

Metamorphic environments

Iowaite occurs in veinlets in serpentinite as an alteration product of serpentine (HOM, Webmin).


At the type locality, Matlock drill core, Sioux county, Iowa, USA, iowaite occurs in veinlets in serpentinised 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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