Magnesite

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Magnesite
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General
Category	Mineral
Chemical formula	magnesium carbonate:MgCO₃
Identification
Color	White
Crystal habit	usually massive, rarely as rhombohedrons or hexagonal prisms
Crystal system	trigonal; bar 3 2/m
Cleavage	[1011] Perfect, [1011] Perfect, [1011] Perfect
Fracture	Brittle - Conchoidal
Mohs Scale hardness	3.5 - 5
Luster	Vitreous
Refractive index	Uniaxial (-) nω=1.508 - 1.510 nε=1.700
Pleochroism	N/A
Streak	white
Specific gravity	3.0 - 3.2
Fusibility	infusible
Solubility	Effervesces in hot HCl
Other Characteristics

Magnesite is magnesium carbonate, MgCO₃. Iron (as Fe²⁺) substitutes for Mg with a complete solution series with siderite, FeCO₃. Calcium, manganese, cobalt, and nickel may also occur in small amounts. Dolomite, (Mg,Ca)CO₃, is almost indistinguishable from magnesite.

Magnesite occurs as veins in and an alteration product of serpentine and other magnesium rich rock types in both contact and regional metamorphic terranes. These magnesites often are cryptocrystalline and contain silica as opal or chert.

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Uses

Magnesite can be used as the lining of furnaces because it is virtually impossible to melt. It can also be used as a catalyst and filler in the production of synthetic rubber and in the preperation of magnesium chemicals and fertilizers.

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