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Topaz

Last updated: April 2026

A hard and durable gemstone available in a wide range of colors.

Topaz has a specific gravity of 3.53 and a refractive index of 1.609–1.643, with a Mohs hardness of 8. It is biaxial +.

Physical & Optical Properties

RI Range1.609–1.643
SG Range3.49–3.57
SG Typical3.53
Hardness (Mohs)8
Crystal SystemOrthorhombic
Optic CharacterDR Biaxial (+)
Birefringence0.008
Dispersion0.014
Fluorescence LWVariable
Fluorescence SWVariable
Chelsea FilterInert
PleochroismModerate
ColorsBlue Violet, Yellow Orange, Red Pink, Brown, Colorless
SpeciesTopaz
Blue VioletYellow OrangeRed PinkBrownColorless

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

Topaz varies 1.609 – 1.643 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 0.008 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. The pair drawn here isone specimen: this species is published at 1.609 – 1.643,and the two edges slide together anywhere across it, betweenthe dashed marks. MEANSThat gap IS the birefringence — and it is the stable part.Where the pair sits varies by 3 printed divisions from stoneto stone, so the gap identifies and the position onlynarrows. Take max minus min across the whole rotation; asingle position understates it. 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.

Through the polariscope

Topaz Blinks 4× per turn (DR) 0° 45° 90° 135° ROTATION BETWEEN CROSSED POLARS Topaz blinks light-dark four times in a full turn. That is doubly refractive. It does NOT tell you uniaxial from biaxial — that is the optic figure, which needs a conoscope. Computed from optic character and transparency in gems.json. A polariscope separates singly refractive, doubly refractive and aggregate — it does not show the optic sign.

Drawn from the optic character and transparency above. A polariscope separates singly refractive, doubly refractive and aggregate; the optic sign needs a conoscope. How to take this reading.

Specific gravity, and what it rules out

Topaz SG 3.49–3.57 WHERE IT SITS, AND WHAT ELSE IS THERE 1.0 2.0 3.0 4.0 5.0 SPECIFIC GRAVITY 12 other species in the table overlap this range, so a reading here narrows the field to 13 rather than naming the stone. Combine it with a refractive index to separate what is left. Computed from the specific-gravity range in gems.json. Hydrostatic weighing — the bench method this site recommends; heavy liquids are toxic and regulated. Faint ticks are the other species in the table.

Drawn from the specific-gravity range above, against every other species in the table. How to take this reading.

Through the dichroscope

Topaz Trichroic — two of three at a time BEST ORIENTATION ROTATED 45° — THE NULL At its best orientation Topaz shows colorless in one window and pale blue in the other. Rotate the instrument 45° and the two windows become IDENTICAL — the null. So "both windows the same" means either the stone is singly refractive or you are holding the instrument at the wrong angle, and the only way to tell is to turn it. Topaz is trichroic: a third colour, pink, appears in a different orientation, and a dichroscope only ever shows two at once. Computed from pleochroism and pleochroic colours in gems.json. Window tints are derived mechanically from the colour words, not chosen; a neutral pair depicts no colour at all.

Drawn from the pleochroism above. Two windows that match mean either no pleochroism or the wrong angle — turn the instrument to tell. How the dichroscope compares.

Key Differentiators

Natural vs. Synthetic

Synthetic topaz is commercially available (Hydrothermal (undetectable by portable instruments)). Distinguishing natural from synthetic typically requires microscopic examination of internal features.

Loupewise Pro includes a two-phase natural vs. synthetic testing protocol for Topaz.

Common Simulants

Commonly Confused With

Commonly confused with: Aquamarine, Citrine, Sapphire, Glass, Chrysoberyl, Cubic Zirconia, Danburite, Fluorite, Padparadscha Sapphire, Phenakite, Rock Crystal, Spessartite Garnet.

Treatments

Related Comparisons

Aquamarine Vs Blue TopazCitrine Vs Topaz

Measurement Guides

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

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

Try Loupewise Free →

Studying for the GIA, FGA, or FEEG practical? Topaz 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 →