Magnesite Identification Guide
How to identify Magnesite, magnesium carbonate, using its white porcelaneous look, hardness, and reaction to warm acid.
Read the full Magnesite encyclopedia entry →
What Magnesite Looks Like
Magnesite is magnesium carbonate (MgCO3). It most commonly occurs as white, compact, porcelain-like masses, though it can also form rhombohedral crystals. It is often confused with howlite and is widely dyed to imitate turquoise.
- Color: white to grayish or yellowish; frequently with gray veining
- Luster: dull to porcelaneous in massive form; vitreous on crystals
- Transparency: opaque (massive) to translucent (crystals)
- Habit: dense porcelaneous nodules ("bone" texture), or rhombohedral/trigonal crystals
Step-by-Step Field ID Checklist
- Note the chalky white, porcelain-like body, often with a network of gray veins.
- Test hardness — Mohs 3.5-4.5; a steel knife scratches it.
- Apply dilute acid — magnesite effervesces only weakly with cold HCl but reacts more strongly when the acid is warm or the sample is powdered (a key carbonate test).
- Check for rhombohedral cleavage in crystalline samples.
- Look for dye in commercial pieces sold as turquoise — color sits in cracks.
Key Diagnostic Tests
- Mohs hardness: 3.5-4.5.
- Streak: white.
- Cleavage: perfect rhombohedral (in crystals).
- Specific gravity: ~3.0.
- Acid: slow fizz in cold dilute HCl, brisk when warmed/powdered — distinguishes from non-carbonates.
Common Look-Alikes and How to Tell Them Apart
- Howlite: very similar white veined look and similar softness, but howlite does NOT effervesce in acid (borate, not carbonate) — the acid test is decisive.
- Calcite: softer would not separate them well, but calcite effervesces vigorously in cold acid, while magnesite reacts only weakly cold.
- Dolomite: also weak cold acid reaction; needs chemical/staining test to separate from magnesite.
- Turquoise (dyed magnesite imitation): real turquoise is harder (5-6) and does not fizz in acid; dyed magnesite is soft and shows dye in veins.
Where It Is Typically Found
Magnesite forms by alteration of magnesium-rich rocks (serpentinite, peridotite) and in some sediments. Major sources include Brazil, China, Austria, Australia, and the USA.
Frequently asked questions
How can you tell if magnesite is real?
Magnesite is white and porcelain-like, Mohs 3.5-4.5, with a white streak, and it effervesces weakly in cold dilute acid but more strongly when warmed or powdered. The carbonate reaction confirms it.
Magnesite vs howlite - how do you tell them apart?
Both are white with gray veining and similar softness, but magnesite is a carbonate that fizzes in acid (especially warm), while howlite is a borate and does not effervesce. The acid test is the key.
Is dyed magnesite sold as turquoise?
Yes. Soft white magnesite is commonly dyed blue to imitate turquoise. Real turquoise is harder (5-6) and does not fizz in acid, while dyed magnesite is soft and shows color concentrated in cracks.
Does magnesite react to acid?
Yes, but unlike calcite it fizzes only weakly in cold dilute HCl; the reaction becomes brisk when the acid is warmed or the magnesite is powdered.
Magnesite identified by the community
Recent Magnesite specimens identified with Rock Identifier.
