Sodalite
Last updated: April 2026
Opaque to translucent blue sodium aluminum silicate chloride; chemically distinct from lapis lazuli (a rock containing lazurite, calcite, and pyrite). Strong orange LW fluorescence and low SG (~2.27 vs lapis ~2.75) are the primary field separations. Hackmanite is a pink/colorless variety showing tenebrescence (reversible color change under UV). Typically lacks the gold pyrite flecks present in lapis lazuli.
Sodalite has a specific gravity of 2.27 and a refractive index of 1.483–1.487, with a Mohs hardness of 5.5–6.0. It is aggregate.
Physical & Optical Properties
Measured with a polariscope, a refractometer, a hydrostatic balance, a Chelsea filter, a UV torch, a loupe, a darkfield loupe and a spectroscope — step-by-step for each.
Through the refractometer
Drawn from the refractive index above, on a 1.40–1.81 scale. How to take this reading.
Related: Sodalite Varieties
Key Differentiators
- Hackmanite variety shows strong orange LW fluorescence (tenebrescence); plain sodalite is inert to LW UV — lapis lazuli shows only weak orange LW
- Very low SG (~2.27) — lapis lazuli averages ~2.75
- No pyrite inclusions — lapis almost always has gold pyrite flecks
- Uniform blue — no calcite matrix or lazurite patches
Common Simulants
- Lapis Lazuli: Lapis: SG ~2.75 (much heavier); weak orange LW fluorescence (vs sodalite's strong orange); pyrite inclusions characteristic; aggregate RI spot ~1.50–1.67 range. Lapis is a rock, sodalite is a mineral.
- Blue Glass: Glass: isotropic; conchoidal fracture; gas bubbles under magnification; SG varies; no fluorescence match.
Commonly Confused With
Commonly confused with: Lapis Lazuli.
Treatments
- Waxing / impregnation — surface stabilization (common for opaque stones)
Measurement Guides
Identifying a sodalite? Loupewise walks through these tests in order — RI, SG, fluorescence, and more.
Try Loupewise Free →Studying for the GIA, FGA, or FEEG practical? Sodalite is one of the 132 species in Loupewise’s drill and exam pool — practice identifying it from its measured properties under timed exam conditions.
Practice exams →