Forsterite is the magnesium-rich endmember of the olivine solid solution series. It is frequently found as transparent yellow-green crystals in ultramafic rocks or thermally metamorphosed limestones, and is the primary mineral component of the gem variety known as Peridot.
Is this forsterite?
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 forsterite with a known reference. Forsterite sits at Mohs 6.5-7, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Forsterite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Forsterite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: green, yellow-green, colorless, white, gray.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: prismatic crystals, granular, massive.
Often confused with
Forsterite vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside forsterite
Minerals reported to co-occur with forsterite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Mg₂SiO₄
- Mohs hardness
- 6.5-7
- Density
- 3.2-3.3 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Orthorhombic
- Crystal habit
- Prismatic Crystals, Granular, Massive
- Cleavage
- Distinct On {010}, Poor On {100}
- Rarity
- Common
- Uses
- Collector, Gemstone, Refractory Material
- Host rock
- Ultramafic Igneous Rocks and Contact Metamorphosed Dolomitic Limestones
- Typical price
- $10-50 per specimen, higher for fine cut gemstones
Where rockhounds find forsterite
Classic worldwide localities
- Norway
- USA (Arizona)
- Myanmar
- Pakistan
- Italy
Field-hunting tip
Look in ultramafic igneous rocks and contact metamorphosed dolomitic limestones country, the host setting where forsterite typically forms. If you start seeing enstatite, chromite, spinel in float, you are in the right ground. Field specimens usually show a prismatic crystals, granular, massive habit, so train your eye for that shape before scanning the outcrop.
Common questions
How do you identify forsterite?+
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How much is forsterite worth?+
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Find forsterite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
