Coesite is a high-pressure polymorph of silica that forms primarily during meteorite impacts or deep-seated subduction events. It is rarely visible to the naked eye and is typically identified by researchers using optical microscopy or X-ray diffraction in samples derived from shock-metamorphosed rocks.
Is this coesite?
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 coesite with a known reference. Coesite sits at Mohs 7.5 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Coesite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Coesite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: colorless, white, gray.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: microscopic crystals, fibrous, granular.
Often confused with
Coesite vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside coesite
Minerals reported to co-occur with coesite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- SiO₂
- Mohs hardness
- 7.5
- Density
- 2.92 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Monoclinic
- Crystal habit
- Microscopic Crystals, Fibrous, Granular
- Cleavage
- Distinct On {110}
- Rarity
- Rare
- Uses
- Collector, Scientific Research
- Host rock
- Impact Metamorphic Rocks, Ultra-high-pressure Metamorphic Terranes
- Typical price
- $50-500 depending on specimen size and locality
Where rockhounds find coesite
Classic worldwide localities
- Meteor Crater, Arizona, USA
- Ries Crater, Germany
- Dora Maira Massif, Italy
- Popigai Crater, Russia
Field-hunting tip
Look in impact metamorphic rocks, ultra-high-pressure metamorphic terranes country — that is the host setting where coesite typically forms. If you start seeing quartz, stishovite, diamond in float, you are in the right ground. Field specimens usually show a microscopic crystals, fibrous, granular habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find coesite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
