copiapite

(mineralogy) Fe₅(SO₄)₆(OH)₂·20H₂O A yellow mineral occurring in granular or scalar aggregates. Also known as ihleite; knoxvillite; yellow copperas. A group of minerals containing hydrous iron sulfates.

Environment

Limited to oxidized iron sulfide deposits in desert climates.

Usually occurs as loose masses of crystalline scales, also in compact granular crusts. No good crystals.

Ocher to sulfur yellow. Luster pearly; hardness 2Ɖ-3; specific gravity 2.1; cleavage micaceous. Piles of shiny flakes; translucent; astringent metallic taste.

Alkaline ferric sulfate (about 25.6% Fe ₂ O ₃ , 38.5% SO ₃ , 30.3% H ₂ O, often with some MgO, CuO, and Al ₂ O ₃ ).

Water-soluble; clear, cold solution becomes and remains cloudy on boiling. Gives magnetic bead on charcoal before the blowpipe.

Difficult to distinguish, without extensive tests, from several similar iron sulfates that resemble it in appearance and occurrence. However, the taste and the water solubility distinguish them from similar appearing minerals of unrelated species. It is also less brilliantly yellow than several oxides of uranium minerals, most of which are brilliantly fluorescent. Becomes magnetic as a roasted bead.

Copiapite is the most common of the ferric sulfates and is selected here as representative of a large group of similar and related species, all of which form in the same fashion. The only reliable method of distinguishing between them is with x-rays. Copiapite is likely to be found in the U.S. wherever pyrite is oxidizing rapidly, as on coal mine refuse piles, or at a burning copper mine in Jerome, Arizona. It has also been noted at Sulphur Bank, California, and in some of the California mercury mines, such as Mt. Diablo. It, or a substitute, continuously formed yellow gobs of gunk in some of the Missouri sinkhole iron sulfide deposits as soon as their pyrite was exposed to the air.

A sample of copiapite

Copiapite is a hydrated iron sulfate mineral with formula: Fe²⁺Fe³⁺₄(SO₄)₆(OH)₂·20(H₂O).

Copiapite forms in the weathering or oxidation zone of sulfide deposits in arid climates. It is soluble in water.

Copiapite was first described in 1833 for an occurrence near Copiapo, Atacama, Chile. It is sometimes known as yellow copperas

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