PYROCHROITE
Class : Oxides and hydroxides
Subclass : Hydroxides and hydrates
Crystal system : Trigonal
Chemistry : Mn(OH)2
Rarity : Uncommon
Pyrochroite is a manganese hydroxide found in deposits of this metal, where it forms following late hydrothermal circulations. Its name comes from the Greek pûr (fire) and khroia (color), because this mineral changes color when heated. Pyrochroite occurs in tabular, rhombohedral or more rarely prismatic crystals of 1 cm at most, but remain rare. Pyrochroite occurs mainly in foliated or cleavable masses exceeding 10 cm and in veinlets intersecting the other manganese minerals associated with it (hausmannite, rhodochrosite, tephroite). It is a mineral of extraordinarily variable color : colorless, bluish, greenish, pink, colors which darken upon exposure to air and light to result in brown-bronze then black hues.
Main photo : Pyrochroite from N'Chwaning II Mine, South Africa © Bruce Cairncross
Pyrochroite in the World
Pyrochroite is not known in the French underground.
Twinning
No twins known for this mineral species.
Fakes and treatments
No fakes listed for this mineral species.
Hardness : 2.5 to 3
Density : 3.23 to 3.27
Fracture : Undetermined
Streak : White
TP : Translucent to opaque
RI : 1.680 to 1.723
Birefringence : 0.040
Optical character : Uniaxial -
Pleochroism : Visible
Fluorescence : None
Solubility : Hydrochloric acid
Magnetism : NoneRadioactivity : None