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Magnesite
Current inventory:  1 gem
 

Chemistry:  MgCO₃

Discovered in 1808;   IMA status: Valid (pre-IMA; Grandfathered).

Magnesite is named after its chemical composition; principally containing Magnesium.

Classification

Mineral Classification:

Carbonates

Strunz 8th Ed. ID:

5/B.02-30

Nickel-Strunz 10th Ed. ID:

5.AB.05

5 : CARBONATES (NITRATES)
A : Carbonates without additional anions, without H₂O
B : Alkali-earth (and other M²⁺) carbonates

Related to:

Calcite Group: Vaterite, Calcite, Magnesite, Siderite, Rhodochrosite, Smithsonite, Spaerocobaltite, Gaspeite, Otavite. Gaspeite-Magnesite Series and Magnesite-Siderite Series.

Crystal Data

Crystallography:

Trigonal - Hexagonal - Scalenohedral

Crystal Habit:

Uncommon as crystals. Crystals usually rhombohedral to 30 cm; rarely prismatic, tabular or scalenohedral. Typically massive, coarse- to fine-granular, very compact and porcelainous; earthy to rather chalky; lamellar; coarsely fibrous.

Twinning:

Unproven

Physical Properties

Cleavage:

[1011] Perfect, [1011] Perfect, [1011] Perfect

Fracture:

Conchoidal

Tenacity:

Brittle

Moh's Hardness:

3.5 - 4.5

Density:

2.98 - 3.02 (g/cm³)

Luminescence:

May exhibit pale green to pale blue fluorescence and phosphorescence under UV; may be Triboluminescent

Radioactivity:

Not Radioactive

Other:

Slightly soluble in water with the solubility increasing with the presence of NaCl, Na2SO4, or CO2.

Optical Properties

Color:

Colorless, white, greyish-white, yellowish, pale green, brown, faintly pink, lilac-rose

Transparency:

Transparent, Translucent

Luster:

Vitreous

Refractive Index:

1.509 - 1.700  Uniaxial ( - )

Birefringence:

0.191

Dispersion:

Very strong

Pleochroism:

Visible

Occurances

Geological Setting:

A primary mineral in igneous or sedimentary rocks; formed by metamorphism or alteration of serpentine and peridotite; uncommon in marine evaporites and hydrothermal veins; rare in carbonatites.

Common Associations:

Antigorite, Calcite, “Chlorite”, Dolomite, Talc

Co-Type Localities:

Magnisía (Magnesia) Prefecture, Thessalia (Thessaly) Department, Greece.
Bettolino, Baldissero Canavese, Canavese District, Torino Province, Piedmont, Italy.

Year Discovered:

1808

View mineral photos:

Magnesite Mineral Photos and Locations

More Information

Mindat.org
Webmineral.com

Magnesite is an extremely rare gem that is a member of the Calcite mineral group that includes Calcite, Siderite, Rhodochrosite, Smithsonite, Spherocobaltite and Gaspeite. Facetable crystals are very rare and faceting is difficult due to its perfect rhombohedral cleavage. Magnesite gems are beautiful with huge birefringence and strong dispersion. Most gems are colorless but may also be yellowish, pale green or faintly pink. The current main source of facet grade crystals is Brumado, Bahia, Brazil.
 

  
Magnesite gems for sale: