Cebollite is a rare calcium aluminum silicate mineral known for its distinct fibrous or needle-like appearance. It is primarily found as a secondary alteration product in igneous rocks, specifically in the Gunnison County area of Colorado where it was first discovered.
Is this cebollite?
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 cebollite with a known reference. Cebollite sits at Mohs ~5, 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: dull.
- 4Match the color rangeCompare against the expected color range: white, colorless, greenish gray, light brown.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: fibrous.
Often confused with
Cebollite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Luster reads dull on Cebollite and silky, subvitreous on Pectolite.
How to tell apart: Luster reads dull on Cebollite and vitreous, pearly on cleavage on Wollastonite.
How to tell apart: Luster reads dull on Cebollite and vitreous to pearly on Natrolite.
Often found alongside cebollite
Minerals reported to co-occur with cebollite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Ca₅Al₂(SiO₄)₃(OH)₄
- Mohs hardness
- ~5
- Density
- 2.96 g/cm³
- Streak
- White
- Luster
- Dull
- Transparency
- Semitransparent
- Crystal system
- Orthorhombic
- Crystal habit
- Fibrous
- Cleavage
- Distinct in one direction
- Rarity
- Rare
- Uses
- Collector
- Host rock
- An alteration product of melilite in a carbonatite (Iron Hill, Colorado, USA); along a diabase-chalk contact (Scawt Hill, Ireland)
Where rockhounds find cebollite
Classic worldwide localities
- Iron Hill and in Cebolla Creek, near Powderhorn, Gunnison Co., Colorado, USA
- Scawt Hill, near Larne, Co. Antrim, Ireland
- Gardiner complex, beyond the head of Kangerdlugssuaq Fjord, Greenland
- Letseng-La-Terai kimberlite, Lesotho
- De Beers diamond mine, Kimberley, Cape Province, South Africa
- Tokatoka district, about 150 km north of Auckland, New Zealand
Field-hunting tip
Where it forms: An alteration product of melilite in a carbonatite (Iron Hill, Colorado, USA); along a diabase-chalk contact (Scawt Hill, Ireland). If you start seeing melilite, natrolite, calcite in float, you are in the right ground. Typical habit: fibrous. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify cebollite?+
Where is cebollite found?+
What rocks look like cebollite?+
What minerals are found with cebollite?+
What kind of rock does cebollite form in?+
What is cebollite used for?+
Find cebollite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
