Andesite is a fine-grained volcanic rock intermediate in composition between basalt and rhyolite. It frequently exhibits a porphyritic texture, with distinct larger crystals of plagioclase or amphibole embedded in a finer groundmass. Collectors look for this rock primarily within subduction zone volcanic chains where it forms significant lava flows and volcanic edifices.
Is this andesite?
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 andesite with a known reference. Andesite sits at Mohs 6-7 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Andesite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Andesite typically shows a dull luster.
- 4Match the color rangeCompare against the expected color range: gray, dark gray, brownish-gray, greenish-gray.
- 5Look at form & habitTypical habit: aphanitic to porphyritic.
Often confused with
Andesite vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside andesite
Minerals reported to co-occur with andesite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Mohs hardness
- 6-7
- Density
- 2.1-2.8 g/cm³
- Streak
- White
- Luster
- Dull
- Transparency
- Opaque
- Crystal habit
- Aphanitic to Porphyritic
- Cleavage
- None
- Rarity
- Common
- Uses
- Construction Aggregate, Road Metal, Decorative Stone
- Host rock
- Volcanic Arcs
- Typical price
- $1-10 per specimen for typical hand samples
Where rockhounds find andesite
1 mapped spotsClassic worldwide localities
- Andes Mountains, South America
- Cascade Range, USA
- Japan
- Indonesia
- New Zealand
Field-hunting tip
Look in volcanic arcs country — that is the host setting where andesite typically forms. If you start seeing plagioclase, pyroxene, hornblende in float, you are in the right ground. Field specimens usually show a aphanitic to porphyritic habit, so train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in Utah — start trip planning there.
Common questions
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Find andesite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
