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Danburite

Last updated: April 2026

Danburite is sometimes sold as a colorless diamond substitute or confused with colorless topaz. The sky-blue LW fluorescence is highly distinctive. Key separator from topaz: SG is only 2.97–3.02 vs topaz 3.49–3.57 — danburite will float in methylene iodide (SG 3.32) while topaz sinks.

Danburite has a specific gravity of 3.00 and a refractive index of 1.627–1.636, with a Mohs hardness of 7.0–7.5. It is biaxial −.

Physical & Optical Properties

RI Range1.627–1.636
SG Range2.97–3.02
SG Typical3.00
Hardness (Mohs)7–7.5
Crystal SystemOrthorhombic
Optic CharacterDR Biaxial (−)
Birefringence0.006
Dispersion0.017
Fluorescence LWStrong blue
Fluorescence SWStrong blue
Chelsea FilterInert
PleochroismNone
ColorsColorless, Yellow Orange, Red Pink
SpeciesDanburite (CaB₂Si₂O₈)
ColorlessYellow OrangeRed Pink

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

Danburite reads 1.629 – 1.634 1.40 1.45 1.50 1.55 1.60 1.65 1.70 1.75 1.80 REFRACTIVE INDEX DORotate the stone through a full 360°, reading both edges atevery 45°. SEETwo boundaries 0.006 apart — so close that at this size theyread as one thick line. On the instrument they separate onlywith a steady head and a sharp edge. MEANSThat gap IS the birefringence. Take max minus min across thewhole rotation — a single position understates it, so onereading is an incomplete one. Computed from gems.json — edge positions are arithmetic, not drawn. RI increases upward; the field above the boundary is the dark one.

Drawn from the refractive index above, on a 1.40–1.81 scale. How to take this reading.

Key Differentiators

Common Simulants

Commonly Confused With

Commonly confused with: Diamond, Topaz.

Treatments

Measurement Guides

How to Identify a GemstoneHow to Measure Specific GravityHow to Use a RefractometerUV Fluorescence Testing

Identifying a danburite? Loupewise walks through these tests in order — RI, SG, fluorescence, and more.

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Studying for the GIA, FGA, or FEEG practical? Danburite is one of the 132 species in Loupewise’s drill and exam pool — practice identifying it from its measured properties under timed exam conditions.

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