Pyrochroite

hydroxide

primary

Formula: Mn2+(OH)2
Hydroxide, brucite group
Specific gravity: 3.25
Hardness: 2½
Streak: White
Colour: Colourless, greenish, bluish (fresh), brown to black (exposed); flesh-red or amethystine in transmitted light
Solubility: Easily soluble in dilute hydrochloric acid
Environments:

Igneous volcanic environments
Metamorphic environments
Hydrothermal environments

Pyrochroite is a primary manganese mineral occurring in some volcanogenic massive sulphide deposits, and also a hydration product of manganosite, in turn metamorphosed from rhodochrosite (HOM), or a secondary mineral after hausmannite (Webmin).
Associated minerals include hausmannite, rhodochrosite, manganosite, galaxite, tephroite, alabandite, lead, baryte, calcite and dolomite (HOM).

At Franklin and Sterling hill, New Jersey, USA, pyrochroite occurs in secondary hydrothermal veinlets cutting franklinite ore, with rhodochrosite, calcite, willemite, gageite, chlorophoenicite and hodgkinsonite (Dana).

Common impurities: Mg

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