Andalusite is a metamorphic mineral common in aluminum-rich rocks, often recognized by its prismatic, squarish crystal habit. The variety chiastolite is well-known for the distinct dark cruciform carbon inclusions visible in cross-sections, making it a favorite for collectors and lapidary work.
Is this andalusite?
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 andalusite with a known reference. Andalusite sits at Mohs 6.5-7.5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: white.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous to subvitreous.
- 4Match the color rangeCompare against the expected color range: reddish-brown, brown, pink, gray, yellow, dark green, red, green.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: blocky, euhedral crystals, prismatic.
Often confused with
Andalusite vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside andalusite
Minerals reported to co-occur with andalusite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Al₂SiO₅
- Mohs hardness
- 6.5-7.5
- Density
- 3.13-3.16 g/cm³
- Streak
- White
- Luster
- Vitreous to subvitreous
- Transparency
- Transparent to nearly opaque with inclusions
- Crystal system
- Orthorhombic
- Crystal habit
- Blocky, euhedral crystals, prismatic
- Cleavage
- Good on {110}, poor on {100}
- Rarity
- Common
- Uses
- Collector, Lapidary, Industrial
- Host rock
- A result of contact metamorphism of argillaceous sediments, also in regionally metamorphosed schists
Where rockhounds find andalusite
8 mapped spotsClassic worldwide localities
- Lancaster, Worcester Co., Massachusetts, USA
- Leiperville, Delaware Co., Pennsylvania, USA
- Custer, Custer Co., South Dakota, USA
- Fresno, Fresno Co., near Ogilby, Cargo Muchacho Mountains, Imperial Co., and near Daltons Ranch, Madera Co., California, USA
- Hornachuelos, near Córdoba, Córdoba Province, Spain
- Lisens Alp, Selraintal, Tirol, Austria
Field-hunting tip
Where it forms: A result of contact metamorphism of argillaceous sediments, also in regionally metamorphosed schists. If you start seeing kyanite, sillimanite, cordierite in float, you are in the right ground. Typical habit: blocky, euhedral crystals, prismatic. Train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in South Carolina, California, Maine. Start trip planning there.
More andalusite photos
Common questions
How do you identify andalusite?+
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Can I find andalusite in the United States?+
What rocks look like andalusite?+
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Find andalusite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
