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 7.5-8, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: white.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous.
- 4Match the color rangeCompare against the expected color range: colorless.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: inclusions.
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
- 7.5-8
- Density
- 2.93 g/cm³
- Colors
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Monoclinic
- Crystal habit
- Inclusions
- Cleavage
- {010} and {012}, suspected
- Rarity
- Rare
- Uses
- Collector, Scientific research
- Host rock
- Formed at pressures in excess of 20 kbar, as fine-grained intergrowths with quartz and silica glass in impact metamorphosed rocks and tektites
Where rockhounds find coesite
Classic worldwide localities
- Meteor Crater, Coconino Co., Arizona, USA
- Nördlinger Ries crater, Bavaria, Germany
- Kara structure, Pay-Khoy, Russia
- Dora-Maira massif, Parigi, near Martiniana Po, Piedmont, Italy
- Grytting, Selje district, Norway
- Wabar craters, Rub' al Khali, Saudi Arabia
Field-hunting tip
Where it forms: Formed at pressures in excess of 20 kbar, as fine-grained intergrowths with quartz and silica glass in impact metamorphosed rocks and tektites. If you start seeing quartz, stishovite, silica glass in float, you are in the right ground. Typical habit: inclusions. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify coesite?+
Where is coesite found?+
What rocks look like coesite?+
What minerals are found with coesite?+
What kind of rock does coesite form in?+
What is coesite used for?+
Find coesite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
