Magnesite is a magnesium carbonate mineral that typically occurs in a massive, earthy habit or as a white, porcellaneous nodule. It is often found as an alteration product in ultramafic rock where magnesium-rich minerals have undergone hydrothermal alteration.
Is this magnesium carbonate?
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 carbonate with a known reference. Magnesium Carbonate 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 Carbonate leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Magnesium Carbonate 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 Carbonate vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside magnesium carbonate
Minerals reported to co-occur with magnesium carbonate. 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
Where rockhounds find magnesium carbonate
1 mapped spotsClassic worldwide localities
- Austria
- Greece
- China
- Brazil
- USA
Field-hunting tip
Look in ultramafic rocks, hydrothermal veins country, the host setting where magnesium carbonate 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
How do you identify magnesium carbonate?+
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Find magnesium carbonate on the map
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