Key properties
| Chemical formula | MgCO3 |
| Crystal system | Trigonal |
| Mohs hardness | 3.5-4.5 |
| Toughness | Poor to fair (brittle, granular) |
| Refractive index | 1.509-1.700 |
| Birefringence | 0.1910 |
| Optic character | Uniaxial negative; gem material reads as an aggregate (AGG) with a strong birefringence blink (-) |
| Specific gravity | 3.00-3.20 |
| Cleavage | Perfect rhombohedral {10-11} in crystals; not seen in massive material |
| Fracture | Granular to uneven |
| Habit | Usually massive, compact and earthy to fine-grained; also botryoidal and, rarely, rhombohedral crystals |
| Lustre | Dull to earthy on fracture surfaces; polish: Vitreous to slightly waxy |
| UV fluorescence | Variable — much gem material is inert, but some fluoresces blue-white (SW) or pale green to blue-white (LW) |
| Pleochroism | None |
| Cause of colour | Natural material is white from the magnesium carbonate itself; grey, yellow and brown tones come from iron-bearing impurities; strong fashion colours are dye |
| Typical inclusions | Grey to dark veining and mottling from other minerals; occasional cellular patterns reminiscent of howlite matrix |
| Stability | Effervesces in hot hydrochloric acid (calcite fizzes in cold acid); stable to light; dyed colour may fade |
| Heat sensitivity | Decrepitates and breaks down under torch heat; keep away from heat |
| Care and cleaning | Warm soapy water and a soft cloth; no ultrasonic, no steam; avoid acids, household chemicals and prolonged immersion |
| Birthstones | None |
| Availability | Widely available as inexpensive dyed beads and cabochons; natural white material moderately available |
| Recognition | White matrix stone, softer than howlite-look turquoise imitations suggest; spot RI about 1.51-1.52 with an unmistakable strong birefringence blink; SG about 3.1; fizzes only in hot acid |
Varieties
Magnesite
| Colour | white to cream, commonly with grey veining; frequently dyed |
| Transparency | opaque |
| Clarity type | Not applicable — massive opaque material |
| Phenomena | None |
| Appearance | Fine-grained porcelain-like white, often with grey spiderweb veining so similar to howlite that the two are routinely confused; dyed pieces show colour pooled in cracks and drill holes |
| Trade names | None standard for undyed material • 'lime' magnesite (marketing) |
| Misnomers | Dyed magnesite sold as turquoise • sold as 'white turquoise' • dyed blue as lapis imitation |
| Typical sizes | Beads 6-20 mm; cabochons of almost any size; large carvings common |
| Cutting styles | Beads • cabochons • carvings • tumbled stones |
| Key separations | vs howlite: magnesite spot RI ~1.51-1.52 with a violent birefringence blink vs howlite ~1.59 with almost none; SG 3.0-3.2 vs 2.45-2.58 • vs turquoise: spot RI and SG both lower than turquoise (1.61-1.65; 2.6-2.9); dye in cracks • vs calcite: calcite effervesces in cold dilute HCl, magnesite only when hot • vs bone/ivory: no organic structure under magnification |
| Sources (localities) | Brazil (Brumado, Bahia — main gem supply) • China and Turkey (bead material and major industrial producers) • Austria (Veitsch, historic) • Greece (type locality) • India (Salem) |
| Availability | Plentiful as cheap dyed beads; natural white cabs readily available |
| Market notes | Almost all bright-coloured magnesite on the market is dyed — disclosure is mandatory; white magnesite is also baked into 'wildhorse' style stones from mixtures |
| Care notes | Very soft and porous — remove before swimming or cleaning; ultrasonic and steam unsafe; wipe with a damp soft cloth |
| In short | Magnesite is the dyed-white-stone trade's other workhorse, interchangeable with howlite in look but instantly separable by its extreme birefringence blink. Soft, porous and cheap, it belongs in fashion jewellery with clear dye disclosure. |
| Size (ct) | USD per carat | Tier | As of |
|---|---|---|---|
| 1.00–100.00 | $0.05 – $0.40 | commercial beads and cabs | 2026-10-26 |
Retail market survey, per carat unless noted. Ranges describe what commercial to fine stones trade at; exceptional stones and provenance premiums sit above them.
Sources
GIA gem encyclopedia · mindat.org · Wikipedia
Data compiled and fact-checked against gemmological literature, October 2026 (JDMIS gem reference). Properties are ranges accepted in gemmological practice; individual stones vary.
See also
Gemstone reference entries: gem #190
Related materials: Calcite
Identification wizard · All 83 materials · Singapore gem labs