Chiastolite is a variety of andalusite characterized by unique, cross-shaped dark inclusions of carbonaceous material or clay. It is primarily sought by collectors for its natural cruciform patterns and is commonly found in low-grade regional metamorphic rocks.
Is this chiastolite?
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 chiastolite with a known reference. Chiastolite 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. Chiastolite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Chiastolite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: gray, yellowish-brown, reddish-brown.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: prismatic crystals with a distinct black carbon cross inclusion.
Often confused with
Chiastolite vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside chiastolite
Minerals reported to co-occur with chiastolite. 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
- 3.1-3.2 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Opaque
- Crystal system
- Orthorhombic
- Crystal habit
- Prismatic Crystals with A Distinct Black Carbon Cross Inclusion
- Cleavage
- Good in Two Directions
- Rarity
- Common
- Uses
- Collector, Lapidary, Jewelry
- Host rock
- Metamorphic Rocks Like Schist and Slate
- Typical price
- $5-30 per specimen
Where rockhounds find chiastolite
1 mapped spotsClassic worldwide localities
- Spain
- Australia
- USA
- China
- France
Field-hunting tip
Look in metamorphic rocks like schist and slate country — that is the host setting where chiastolite typically forms. If you start seeing quartz, mica, garnet in float, you are in the right ground. Field specimens usually show a prismatic crystals with a distinct black carbon cross inclusion habit, so train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in Massachusetts — start trip planning there.
Common questions
How do you identify chiastolite?+
Where is chiastolite found?+
Can I find chiastolite in the United States?+
How much is chiastolite worth?+
What rocks look like chiastolite?+
What minerals are found with chiastolite?+
What kind of rock does chiastolite form in?+
What is chiastolite used for?+
Find chiastolite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
