Transparent, gem-quality magnesite is rare and beautiful, with colors ranging from colorless, white, and grey to a yellowish brown. This material is relatively difficult to cut. Faceted magnesite is rarely seen. Cabochons are more common.
The International Gem Society (IGS) has a list of businesses offering gemstone appraisal services.
|Crystallography||Hexagonal (R). Crystals very rare (rhombs); massive, compact, fibrous.|
|Colors||Colorless, white, gray, yellowish to brown.|
|Luster||Vitreous to dull.|
|Cleavage||Perfect rhombohedral; brittle.|
|Luminescence||See "Identifying Characteristics" below.|
|Transparency||Transparent to opaque.|
|Optics||o = 1.700-1.717; e = 1.509-1.515. Uniaxial (-).|
|Etymology||After the magnesium (Mg) in its composition.|
|Occurrence||Alteration product of magnesium-rich rocks; sedimentary deposits; as a gangue mineral in hydrothermal ore deposits.|
Even in small stones, magnesite’s strong birefringence is obvious. Larger faceted gems have a sleepy or “fuzzy” look, due to the doubling of back facets as seen through the table facet.
- Effervesces in warm acids.
- Luminesces blue, green, or white under shortwave (SW) ultraviolet light. Green phosphorescence is not uncommon.
Magnesite accepts dye treatments very well due to its porousness. Since cabochon or bead shapes are common, dyed specimens are sometimes sold as turquoise. If the material is disclosed as treated or a turquoise simulant, this is an acceptable practice. If not, buyer beware.
Facetable crystals come only from Brazil.
- Brumado, Bahia, Brazil: Magnificent and large rhomb shaped crystals, often transparent, colorless.
- Algeria; Austria, India; Korea; Norway; South Africa; Zaire.
The Smithsonian Institution holds the largest known cut magnesite, a 390-carat cushion-step gem from Brazilian material. Most gem-quality material occurs in sizes under 10-15 carats.
Due to magnesite’s very low hardness, gems and jewelry made from this material should be stored in a cloth bag or box, away from other gems. Harder gems could scratch them. (A knife could scratch the surface of most of these stones). Consult our gemstone jewelry cleaning guide for more care recommendations.
The National Institute for Occupational Safety and Health (NIOSH) has guidelines for exposure to this mineral. As a powder, it can irritate the skin, eyes, and respiratory system.