Gemstone Glossary

Magnesite

Magnesite is commonly found in white or gray and sometimes tinted yellow or brown. Individual crystals are vitreous and translucent to transparent. However, they more commonly occur in groupings and as cleavage fragments that are dull in luster. The most common crystal form is in massive, compact, porous masses as well as grainy and in groups of thin, prismatic needles. Good crystals are extremely rare.


Magnesite is composed of magnesium, carbon, and oxygen (MgCO3) and was named after its chemical composition. Breunnerite or Ferro-magnesite is a named used to specify its iron rich variety. Magnesite ranks 3.5 to 4.0 on the Moh’s Scale of Hardness with a Specific Gravity of approximately 3.0. Magnesite is commonly found associated with Calcite, Dolomite, Aragonite, Strontianite and Serpentine.

First discovered in 1808 in Greece, occurrence of Magnesite has been reported in several locations worldwide. The deposits in Styria and Zillertal in Austria are known to produce fine quality crystals. Recently, an interesting form of Magnesite has been unearthed in Bahia, Brazil. The deposit produces clear, transparent, six-sided Magnesite crystals resembling the Iceland Spar variety of Calcite. Such crystals have never been found before and although identical in appearance to the Calcite variety, they are much rarer and highly sought after. The common Iceland Spar Calcite is sometimes wrongly labeled by some unscrupulous dealers as Magnesite to stimulate sales.

Magnesite does not ordinarily form good crystals, but can make up a substantial portion of some rock types. It is commonly collected as a rare mineral and sometimes faceted into a gemstone.