Andalusite
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.
About Andalusite
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.
Identifying a andalusite? GemID walks through these tests in order — RI, SG, fluorescence, and more.
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