Cristobalite is a high-temperature polymorph of silica that often forms small, white, snowball-like aggregates within vesicles of volcanic rocks like rhyolite. Collectors should look for distinct pseudo-cubic or octahedral crystals lining cavities in volcanic flows. It is most famously associated with obsidian flows where it forms the characteristic white spots known as snowflake obsidian.
Is this cristobalite?
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 cristobalite with a known reference. Cristobalite sits at Mohs 6.5 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Cristobalite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Cristobalite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: white, colorless, gray, pale yellow.
- 5Look at form & habitCrystal system: tetragonal. Typical habit: octahedral, pseudo-cubic crystals, spherulites, granular masses.
Often confused with
Cristobalite vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside cristobalite
Minerals reported to co-occur with cristobalite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- SiO₂
- Mohs hardness
- 6.5
- Density
- 2.32 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Tetragonal
- Crystal habit
- Octahedral, Pseudo-cubic Crystals, Spherulites, Granular Masses
- Cleavage
- None
- Rarity
- Uncommon
- Uses
- Collector, Scientific Research, Catalyst Carrier
- Host rock
- Rhyolite, Andesite, Obsidian
- Typical price
- $10-50 for small cabinet specimens
Where rockhounds find cristobalite
Classic worldwide localities
- Mexico
- USA
- Germany
- Italy
- France
Field-hunting tip
Look in rhyolite, andesite, obsidian country — that is the host setting where cristobalite typically forms. If you start seeing quartz, tridymite, feldspar in float, you are in the right ground. Field specimens usually show a octahedral, pseudo-cubic crystals, spherulites, granular masses habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find cristobalite on the map
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