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 6-7, 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: white, blue gray, brown, gray, yellow.
- 5Look at form & habitCrystal system: tetragonal. Typical habit: crystalline, spherical.
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
- 6-7
- Density
- 2.32-2.36 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Tetragonal
- Crystal habit
- Crystalline, spherical
- Cleavage
- None
- Fluorescence
- Green red under SW UV; green red under LW UV
- Rarity
- Uncommon
- Uses
- Collector, Scientific research, Catalyst carrier
- Host rock
- In vesicles and lithophysae; a late-crystallizing phase in basaltic to rhyolitic volcanic rocks; from acid-sulfate-type hydrothermal alteration of volcanic rocks; precipitated by hot springs
Where rockhounds find cristobalite
Classic worldwide localities
- Glass Mountain, Little Lake, and Sugarloaf Mountain, near Coso Hot Springs, Inyo Co., California, USA
- Crater Lake, Klamath Co., Oregon, USA
- Mayen and Mendig, Eifel district, Germany
- Sárospatak, Hungary
- Ellora Caves, Maharashtra, India
- Tokatoka district, about 150 km north of Auckland, New Zealand
Field-hunting tip
Where it forms: In vesicles and lithophysae; a late-crystallizing phase in basaltic to rhyolitic volcanic rocks; from acid-sulfate-type hydrothermal alteration of volcanic rocks; precipitated by hot springs. If you start seeing tridymite, quartz, sanidine in float, you are in the right ground. Typical habit: crystalline, spherical. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify cristobalite?+
Where is cristobalite found?+
What rocks look like cristobalite?+
What minerals are found with cristobalite?+
What kind of rock does cristobalite form in?+
What is cristobalite used for?+
Find cristobalite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
