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, 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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