Identification guide · Minerals
How to Identify Andalusite
Andalusite typically appears as thick, squarish prisms with a nearly square cross-section, often pink-brown, gray, or olive-green, with a vitreous luster and a colorless to white streak. Hardness around 7.5 helps separate it from softer look-alikes, and it shows distinct pleochroism, appearing to change color slightly as a crystal is rotated in light. The chiastolite variety reveals a dark carbonaceous cross when a prism is cut and polished perpendicular to its length, a feature unique enough to prevent confusion with kyanite or sillimanite.
Andalusite identification checklist
| Color | Reddish brown, Olive green, Gray, Pink | Look at a clean, dry surface in daylight. Color zoning, banding or spots are as diagnostic as the hue. |
|---|---|---|
| Luster | Vitreous | Fresh surfaces shine like glass; a dull surface usually means weathering, so chip or wet a corner. |
| Transparency | Transparent to translucent | Hold a thin edge up to a bright light and note whether light passes through. |
| Mohs hardness | 6.5–7.5 | It scratches glass and a steel knife and cannot be scratched by a steel file. |
| Streak | White | Drag a corner across unglazed porcelain (the back of a bathroom tile) and check the powder color. |
| Cleavage | Good prismatic, two directions at ~89° | |
| Fracture | Uneven to subconchoidal | Broken surfaces show smooth, curved, shell-like scoops. |
| Specific gravity | 3.13–3.21 | Heavier than it looks (specific gravity about 3.17). |
| Crystal system | Orthorhombic |
Extra tests for Andalusite
Glass check. Andalusite shares a glassy luster and conchoidal fracture with man-made glass. Glass sits near Mohs 5.5 and often contains round gas bubbles, so a hardness test and a hand lens separate them.
Andalusite look-alikes and how to tell them apart
Both sit near Mohs 6.5–7.5, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Andalusite vs Feldspar →
Both sit near Mohs 6.5–7.5, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Andalusite vs Quartz →
Both sit near Mohs 6.5–7.5, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Andalusite vs Axinite →
Chrysoberyl is harder (Mohs 8.5) than Andalusite (Mohs 6.5–7.5), so Chrysoberyl will scratch Andalusite and not the other way round. It scratches glass and a steel knife and cannot be scratched by a steel file. Andalusite vs Chrysoberyl →
Andalusite identification FAQ
How can you tell if a rock is Andalusite?
Check the color (reddish brown, olive green, gray, and pink), the vitreous luster, a Mohs hardness of 6.5–7.5 and a white streak. Photographing it with the StoneSnap app gives a match in seconds.
What is the hardness of Andalusite?
Andalusite has a Mohs hardness of 6.5–7.5. It scratches glass and a steel knife and cannot be scratched by a steel file.
What is the difference between Andalusite and Feldspar?
Andalusite (Mohs 6.5–7.5, vitreous luster) and Feldspar (Mohs 6–6.5, vitreous to pearly luster) look alike, but hardness, streak and heft usually separate them. See the full Andalusite vs Feldspar comparison for a side-by-side table.
Is Andalusite worth anything?
Entry-level Andalusite specimens sell for around $2, typical collector pieces about $20, and premium examples $150 or more depending on size, quality and locality.
What color is Andalusite?
Andalusite is most often reddish brown, olive green, gray, and pink. Color varies with impurities and locality, so confirm with hardness and luster rather than color alone.
