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, 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.
