Magnesite

Magnesite is a white, porcelain-like or chalky carbonate mineral made of magnesium and carbon (MgCO₃). It resembles calcite, but it most often occurs as fine-grained, hard, dull masses. Its main importance is as the raw material of heat-resistant (refractory) bricks and of magnesium compounds. Because it takes up dye easily, it is also made into beads and sometimes sold dyed blue as “turquoise”.

Refractory bricks: More than 90% of the magnesite mined is fired to caustic-calcined or sintered magnesite. These products are used in the heat-resistant (refractory) bricks lining steel, cement, glass and copper furnaces. Magnesium compounds: It is the raw material of magnesium oxide and other magnesium compounds, used in medicines, fertilisers and animal feed, paper, sugar, rubber and insulation, among many other things. Flooring: Fired magnesite serves as the binder in magnesia screed, a type of floor covering. Beads and jewellery: It is cut, drilled and polished into beads.

It has a hardness of 3.5–4.5 on the Mohs scale. A fingernail cannot scratch it, but a steel knife can. Its specific gravity is 3–3.2 g/cm³.

Its best-known localities: Haicheng–Dashiqiao belt, Liaoning, China; Brumado, Serra das Éguas, Bahia, Brazil; Satka, Chelyabinsk Oblast, Russia; West of Eskişehir (Tutluca–Yukarıkartal–Ballık area), Türkiye; Kütahya (Sobran–Türkmentepe area), Türkiye.

Known localities in Türkiye: West of Eskişehir (Tutluca–Yukarıkartal–Ballık area), Türkiye; Kütahya (Sobran–Türkmentepe area), Türkiye; Meram–Çayırbağı, Konya, Türkiye.

White, cream or grey; very often a dull, fine-grained, hard mass that looks like unglazed porcelain or chalk. Its rare large crystals are rhomb-shaped. Mohs hardness is 3.5–4.5: a steel knife scratches it, but it cannot scratch glass. Fine-grained masses break with a curved, shell-like fracture; with a density of about 3 it feels slightly heavier than a piece of calcite of the same size. White calcite, dolomite and howlite can look like magnesite. Calcite fizzes at once in cold dilute acid and magnesite does not; howlite does not fizz either but is clearly lighter (density around 2.5–2.6).

On the “street to diamond” value ladder it sits on step 3 of nine: Building and industrial stone. Magnesite is an industrial raw material bought and sold by the ton. Its value depends on its magnesium oxide (MgO) content and the scarcity of harmful impurities: for refractory bricks, cryptocrystalline (gel) magnesite should contain at most about 1% silica (SiO₂), 1.5% calcium oxide and 0.5% iron oxide, and ore that meets these limits is worth much more than ordinary ore. The size of the deposit, how easily the ore is mined and concentrated, the cost of calcining and the distance to factories also matter. As a bead and jewellery material magnesite is inexpensive; whether it has been dyed, and whether that is disclosed, affects its worth, and for large, transparent crystal specimens size and clarity do.

Crystal therapy practitioners and stone sellers claim that white magnesite is calming and brings deep peace and quiet relaxation during meditation. The same sources say magnesite opens the “heart chakra” and gives a sense of happiness and self-love. There is no controlled study showing that magnesite calms people or affects emotions; any relaxation comes from meditating and taking a quiet moment. Wearing or holding the stone does not give the body magnesium; anyone who suspects a magnesium deficiency should see a doctor. Grinding the stone and swallowing it is not advisable either: natural magnesite often contains impurities such as iron and silica, and mining dust should not be breathed. This section reports beliefs; it is not health information. There is no scientific evidence for these claims and no stone replaces medical treatment.

Magnesite is harmless to handle. The fine dust from mines and calcining plants should not be breathed for long, and a dust mask should be used for dusty work. In the United States, the safety agency OSHA sets limits of 15 mg/m³ for total dust and 5 mg/m³ for respirable dust over an eight-hour working day.