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Low-Type Zircon

Last updated: April 2026

A type of zircon whose crystal structure has been damaged by radioactive elements.

Low-Type Zircon has a specific gravity of 4.00 and a refractive index of 1.780–1.815, with a Mohs hardness of 6. It is singly refractive.

Physical & Optical Properties

RI Range1.780–1.815
SG Range3.90–4.10
SG Typical4.00
Hardness (Mohs)6
Crystal SystemTetragonal
Optic CharacterSR (Singly Refractive)
Dispersion0.038
Fluorescence LWInert
Fluorescence SWInert
Chelsea FilterInert
PleochroismWeak
ColorsGreen, Brown, Yellow Orange
SpeciesZircon
GreenBrownYellow Orange

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

Low-Type Zircon varies 1.780 – 1.815 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°, watching the boundary. SEEOne boundary that does not move as you rotate. Where it sitsis not fixed for this species, though: published at 1.780 –1.815, and the stone drawn here reads 1.797 — the dashedmark is the one end of that range this scale can show. MEANSSingly refractive — a stationary single edge through thewhole rotation says so. The value itself is only anarrowing: this species spans 3 printed divisions, so areading places your stone inside the range rather thannaming it. The top of that range is past the 1.81 ceiling,so some stones of this species give no reading at all. 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.

Zircon

Key Differentiators

Treatments

Measurement Guides

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

Identifying a low-type zircon? Loupewise walks through these tests in order — RI, SG, fluorescence, and more.

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Studying for the GIA, FGA, or FEEG practical? Low-Type Zircon 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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