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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.

Through the polariscope

Low-Type Zircon Dark throughout (SR) 0° 45° 90° 135° ROTATION BETWEEN CROSSED POLARS Low-Type Zircon stays dark through the whole rotation. That is singly refractive: there is no second ray to rotate the plane of vibration back into the analyser. 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

Low-Type Zircon SG 3.90–4.10 WHERE IT SITS, AND WHAT ELSE IS THERE 1.0 2.0 3.0 4.0 5.0 SPECIFIC GRAVITY 15 other species in the table overlap this range, so a reading here narrows the field to 16 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

Low-Type Zircon weak — colours not recorded COLOURS NOT IN OUR SOURCE Low-Type Zircon is recorded as showing weak pleochroism, but our source does not name the two colours, so this figure does not paint them. The windows will differ; which hues they take is not something we hold. 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.

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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