Magnesite

Magnesite is magnesium carbonate (MgCO3), a member of the calcite group. In its common massive form it is a porous, chalky white-to-buff material, often crisscrossed by grey to brown veins, making it visually similar to howlite.

Because it is light-colored, porous, and inexpensive, magnesite is frequently dyed to imitate turquoise, lapis, coral, and other gem materials, and is sold widely as beads and tumbled stones.

Magnesite is also an important industrial raw material for magnesium and refractory products. It crystallizes in the trigonal system, though well-formed crystals are far less common than the massive variety.

Magnesite forms in several geological settings. Much commercial magnesite develops where magnesium-rich rocks such as serpentinite and other ultramafic rocks are altered by carbon dioxide-bearing fluids, replacing the original minerals with magnesium carbonate.

It also forms in sedimentary settings, precipitating in magnesium-rich lakes and from the alteration of dolomite and limestone, and as crusts and nodules in weathered ultramafic terrain.

Major producers include China, Russia, Brazil, Austria, Slovakia, and Australia. The massive, cauliflower-textured 'bone' magnesite used for beads is widespread in altered serpentinite regions.

Magnesite is typically chalky white to buff with grey or brown veining, a hardness of about 3.5-4.5 (scratched by a steel knife), white streak, and dull to vitreous luster in massive form.

It is easily confused with howlite; both are white with dark veins and are commonly dyed. Howlite is slightly softer; chemical and density tests distinguish them. Unlike calcite, magnesite usually does NOT fizz in cold dilute hydrochloric acid (it reacts only when warm or powdered), a useful field test.

Dyed magnesite imitating turquoise can be spotted by dye concentrated in veins and surface cracks, and color that may rub off with acetone, plus the lighter weight and lower hardness compared with genuine turquoise.

Industrially, magnesite is the chief ore for magnesium metal and magnesium compounds, and when calcined it produces magnesia used in refractory bricks, cements, and furnace linings.

In the gem and craft trade, natural and dyed magnesite is sold as beads, cabochons, and tumbled stones, often as an affordable turquoise imitation. It takes dye and polish readily.

Metaphysically, magnesite is associated with relaxation and meditation, a spiritual rather than scientific use. Buyers should note that much blue 'turquoise' on the market is actually dyed magnesite or howlite.