Magnesite Value, Price, and Jewelry Information

Magnesite: Brazil (134.5 cts). Photo © Joel E. Arem, PhD, FGA. Used with permission.

Magnesite

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.

Magnesite Information

Data Value
Name Magnesite
Colors Colorless, white, gray, yellowish to brown.
Crystallography Hexagonal (R). Crystals very rare (rhombs); massive, compact, fibrous.
Refractive Index 1.509-1.717
Luster Vitreous to dull.
Hardness 3.5-4.5
Fracture Conchoidal
Specific Gravity 3.0-3.12
Birefringence 0.191-0.202
Cleavage Perfect rhombohedral
Luminescence Luminesces blue, green, or white under shortwave (SW) ultraviolet light. Green phosphorescence is not uncommon.
Luminescence Present Yes
Luminescence Type Fluorescent, Phosphorescent, UV-Short
Enhancements Dyeing.
Typical Treatments Dyeing
Transparency Transparent to opaque.
Formula

MgCO3

Optics

o = 1.700-1.717; e = 1.509-1.515. Uniaxial (-).

Optic Sign 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.

magnesite - rock

“Magnesite – Grenville Front area of western Quebec, Canada,” 9.9 cm across, a monocrystalline magnesite rock (known as magnesitite), by James St. John. Licensed under CC By 2.0.

Comments

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.

Identifying Characteristics

  • Effervesces in warm acids.
  • Luminesces blue, green, or white under shortwave (SW) ultraviolet light. Green phosphorescence is not uncommon.

Enhancements

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.

Magnesite - dyed

Dyed, stabilized magnesites. A great deal of this material has been sold recently at Tucson gem shows. Stones courtesy of Stone Group Lab. © Bear Williams, Stone Group Labs. Used with permission.

Sources

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.

Sizes

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.

Care

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.