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, 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?+
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Find vermiculite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
