Perlite is an amorphous volcanic glass that has a relatively high water content and forms through the hydration of obsidian. It is easily identified by its distinct concentric, onion-like fracture pattern known as perlitic structure, which causes it to shatter into small, spherical beads upon processing.
Is this perlite?
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 perlite with a known reference. Perlite sits at Mohs 5-5.5 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Perlite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Perlite typically shows a pearly luster.
- 4Match the color rangeCompare against the expected color range: gray, white, greenish, brown.
- 5Look at form & habitTypical habit: massive.
Often confused with
Perlite vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside perlite
Minerals reported to co-occur with perlite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Mohs hardness
- 5-5.5
- Density
- 2.2-2.4 g/cm³
- Streak
- White
- Luster
- Pearly
- Transparency
- Opaque
- Crystal habit
- Massive
- Cleavage
- None
- Rarity
- Common
- Uses
- Industrial, Horticultural, Construction
- Host rock
- Volcanic Rhyolitic Flows
- Typical price
- $5-20 per sample
Where rockhounds find perlite
1 mapped spotsClassic worldwide localities
- Greece
- United States
- Turkey
- Italy
- Japan
Field-hunting tip
Look in volcanic rhyolitic flows country — that is the host setting where perlite typically forms. If you start seeing obsidian, rhyolite in float, you are in the right ground. Field specimens usually show a massive habit, so train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in Colorado — start trip planning there.
Common questions
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Find perlite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
