Andalusite
Last updated: April 2026
Strong trichroism (green, red-brown, yellow-orange) is the primary diagnostic; color variation is often visible without instruments. The chiastolite variety contains a black cross-shaped pattern of carbonaceous inclusions.
Physical & Optical Properties
RI Range1.629–1.649
SG Range3.13–3.21
SG Typical3.17
Hardness (Mohs)7–7.5
Crystal SystemOrthorhombic
Optic CharacterDR Biaxial (−)
Birefringence0.010
Dispersion0.016
Fluorescence LWInert
Fluorescence SWInert
Chelsea FilterInert
PleochroismStrong Trichroic
ColorsGreen, Brown, Yellow Orange
SpeciesAndalusite (Al₂SiO₅)
Key Differentiators
- Striking trichroism: green / red-brown / yellow-orange, often visible to naked eye
- Chiastolite variety shows diagnostic black cross-shaped inclusions
- RI 1.629–1.649 — distinguishable from tourmaline (1.624–1.644)
- Biaxial negative; SG 3.13–3.21
Price Context
Natural — low ($/ct)$20
Natural — high ($/ct)$300
NotePer carat; collector and jewelry market
Price context is approximate. GemID is not an appraisal tool. Results are indicators, not certified valuations.
Measurement Guides
Identifying an andalusite? GemID walks through these tests in order — RI, SG, fluorescence, and more.
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