RocksdayAndalusite vs Staurolite
How to tell them apart
An aluminum silicate of metamorphic rocks. Its variety chiastolite shows a dark cross in cross-section.
Photo: Ivar Leidus, CC BY-SA 4.0
A brown metamorphic mineral whose twinned crystals often cross at 90° or 60°, forming natural crosses.
Photo: Robert M. Lavinsky, CC BY-SA 3.0
Quick tests
- Streak (rub on unglazed porcelain): Andalusite leaves a white streak; Staurolite leaves white to gray.
Key differences
- Staurolite crystals cross each other on the outside, not inside.
Side by side
| Property | Andalusite | Staurolite |
|---|---|---|
| Type | Mineral | Mineral |
| Mohs hardness | 6.5–7.5 | 7–7.5 |
| Luster | Vitreous | Vitreous to resinous |
| Streak | White | White to gray |
| Colors | Brown, Pink, Green, Gray | Brown |
| Crystal system | Orthorhombic | Monoclinic |
| Specific gravity | 3.13–3.21 | 3.74–3.83 |
| Formula | Al₂SiO₅ | Fe₂Al₉Si₄O₂₃(OH) |
| Found in | Andalusia, Spain; Minas Gerais, Brazil | Fairy Stone State Park, Virginia; Fannin County, Georgia |
Properties that are the same for both are grayed out.
How to identify andalusite
- Square prisms, often with a black cross inside (chiastolite).
- Gems flash green and red-brown from different angles.
- Hardness about 7.
Crystal system: Orthorhombic
Full Andalusite guide →How to identify staurolite
- Reddish-brown prisms, often crossed like an X or +.
- Hard — scratches glass.
- Usually embedded in mica schist.
- Rough, dull surface on weathered crystals.
Crystal system: Monoclinic
Full Staurolite guide →More comparisons
Could you tell them apart from a blurry close-up?
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