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Formula: Mn2+(OH)2
Hydroxide of manganese,
brucite group
Crystal System: Trigonal
Specific gravity: 3.23 to 3.27 measured, 3.25 calculated
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
Common impurities: Mg
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).
Localities
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).
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