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 — that is 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
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Find forsterite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
