Cordierite is a magnesium-aluminum silicate commonly found in metamorphic rocks subjected to high-grade regional metamorphism. It is famous for its strong pleochroism, often appearing deep violet-blue when viewed from one direction and pale yellow or colorless from another.
Is this cordierite?
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 cordierite with a known reference. Cordierite sits at Mohs 7-7.5 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Cordierite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Cordierite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: blue, violet, gray, colorless, yellow.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: short prismatic crystals, granular, massive.
Often confused with
Cordierite vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside cordierite
Minerals reported to co-occur with cordierite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Mg₂Al₄Si₅O₁₈
- Mohs hardness
- 7-7.5
- Density
- 2.53-2.66 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Orthorhombic
- Crystal habit
- Short Prismatic Crystals, Granular, Massive
- Cleavage
- Distinct in One Direction
- Rarity
- Common
- Uses
- Gemstone, Collector, Lapidary
- Host rock
- Metamorphic Rocks Like Gneiss and Schist
- Typical price
- $10-50 per carat for gem quality, $5-100 for mineral specimens
Where rockhounds find cordierite
2 mapped spotsClassic worldwide localities
- Sri Lanka
- Madagascar
- India
- Brazil
- Norway
Field-hunting tip
Look in metamorphic rocks like gneiss and schist country — that is the host setting where cordierite typically forms. If you start seeing quartz, biotite, sillimanite in float, you are in the right ground. Field specimens usually show a short prismatic crystals, granular, massive habit, so train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in Connecticut, Utah — start trip planning there.
Common questions
How do you identify cordierite?+
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Find cordierite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
