A compact nodule of Magnesite.
Rhombohedral crystal of Magnesite
measuring about 2" from left to right.
CHEMISTRY MgCO3 Magnesium carbonate
CRYSTALLOGRAPHY Hexagonal
CRYSTAL GROWTH AND HABITS Individual crystals are rare for magnesite but when they form they are rhombohedral or scalenohedral. Magnesite commonly is massive, fine to coarse granular and earthy. It sometimes produces compact porcelaneous masses.
COLOR AND OTHER OPTICAL PROPERTIES White, translucent
HARDNESS 3.5 - 5
SPECIFIC GRAVITY 3.0-3.2
LUSTER Vitreous to dull
STREAK White
BREAKABILITY Crystals have rhombohedral cleavage otherwise the massive varieties have an uneven fracture.
OCCURRENCE Magnesite normally is a secondary mineral produced by the alteration of magnesium rich rocks like serpentine or peridotite.
ASSOCIATED MINERALS Calcite, Dolomite