Vermiculite is a hydrated magnesium aluminum iron silicate mineral that forms through the alteration of phlogopite or biotite. It is well-known for its ability to expand significantly when heated, a property that makes it useful in gardening and industrial insulation, though collectors primarily seek it for its distinctive platy, micaceous crystal habits.
Is this vermiculite?
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 vermiculite with a known reference. Vermiculite sits at Mohs 1.5-2 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Vermiculite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Vermiculite typically shows a pearly luster.
- 4Match the color rangeCompare against the expected color range: brown, yellow-brown, golden-yellow, greenish.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: lamellar, micaceous, massive, platy.
Often confused with
Vermiculite vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside vermiculite
Minerals reported to co-occur with vermiculite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- (Mg,Fe,Al)₃(Al,Si)₄O₁₀(OH)₂·4H₂O
- Mohs hardness
- 1.5-2
- Density
- 2.3-2.7 g/cm³
- Streak
- White
- Luster
- Pearly
- Transparency
- Translucent
- Crystal system
- Monoclinic
- Crystal habit
- Lamellar, Micaceous, Massive, Platy
- Cleavage
- Perfect Basal
- Rarity
- Common
- Uses
- Industrial, Horticultural, Insulation
- Host rock
- Ultramafic Rocks, Hydrothermal Deposits
- Typical price
- $5-30 for specimen-grade pieces
Where rockhounds find vermiculite
4 mapped spotsClassic worldwide localities
- USA
- South Africa
- Brazil
- China
- Russia
Field-hunting tip
Look in ultramafic rocks, hydrothermal deposits country — that is the host setting where vermiculite typically forms. If you start seeing phlogopite, apatite, serpentine in float, you are in the right ground. Field specimens usually show a lamellar, micaceous, massive, platy habit, so train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in North Carolina, Georgia, Montana — start trip planning there.
Common questions
How do you identify vermiculite?+
Where is vermiculite found?+
Can I find vermiculite in the United States?+
How much is vermiculite worth?+
What rocks look like vermiculite?+
What minerals are found with vermiculite?+
What kind of rock does vermiculite form in?+
What is vermiculite used for?+
Find vermiculite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
