Magnesite is a magnesium carbonate mineral that typically occurs in massive, earthy habits or as white, porcellaneous nodules. It is often found as an alteration product in ultramafic rocks where magnesium-rich minerals have undergone hydrothermal alteration.
Is this magnesium carbonates?
5-step field checkRun through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.
- 1Test the hardnessTry to scratch magnesium carbonates with a known reference. Magnesium Carbonates sits at Mohs 3.5-4.5 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Magnesium Carbonates leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Magnesium Carbonates typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: white, colorless, gray, yellow, brown.
- 5Look at form & habitCrystal system: trigonal. Typical habit: rhombohedral crystals, massive, botryoidal.
Often confused with
Magnesium Carbonates vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside magnesium carbonates
Minerals reported to co-occur with magnesium carbonates. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- MgCO₃
- Mohs hardness
- 3.5-4.5
- Density
- 3.0 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Trigonal
- Crystal habit
- Rhombohedral Crystals, Massive, Botryoidal
- Cleavage
- Perfect Rhombohedral
- Rarity
- Common
- Uses
- Industrial, Collector, Refractories
- Host rock
- Ultramafic Rocks, Hydrothermal Veins
- Typical price
- $5-50 for cabinet specimens
Where rockhounds find magnesium carbonates
1 mapped spotsClassic worldwide localities
- Austria
- Greece
- China
- Brazil
- USA
Field-hunting tip
Look in ultramafic rocks, hydrothermal veins country — that is the host setting where magnesium carbonates typically forms. If you start seeing calcite, dolomite, serpentine in float, you are in the right ground. Field specimens usually show a rhombohedral crystals, massive, botryoidal habit, so train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in Nevada — start trip planning there.
Common questions
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Find magnesium carbonates on the map
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