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.
- 2Read the textureLook at a fresh break with a hand lens. Grain size: Glassy (amorphous).
- 3Pick out the mineralsComposition: Volcanic glass with a relatively high water content, typically hydrated obsidian. Identify the two or three most abundant grains.
- 4Read the lusterHold the specimen under a strong light. Luster: pearly.
- 5Match the color rangeCompare against the expected color range: gray, white, greenish, brown.
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
- Luster
- Pearly
- Transparency
- Opaque
- Rarity
- Common
- Uses
- Industrial, Horticultural, Construction
- Host rock
- volcanic rhyolitic flows
- Grain size
- Glassy (amorphous)
- Composition
- Volcanic glass with a relatively high water content, typically hydrated obsidian
Where rockhounds find perlite
1 mapped spotsClassic worldwide localities
- Greece
- United States
- Turkey
- Italy
- Japan
Field-hunting tip
Where it forms: volcanic rhyolitic flows. If you start seeing obsidian, rhyolite in float, you are in the right ground. In the U.S., the densest reported localities are in Colorado. Start trip planning there.
Common questions
How do you identify perlite?+
Where is perlite found?+
Can I find perlite in the United States?+
What rocks look like perlite?+
What minerals are found with perlite?+
What kind of rock does perlite form in?+
What is perlite used for?+
Find perlite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
