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Cubic Zirconia

Last updated: April 2026

Cubic zirconia (ZrO2) is entirely synthetic — no natural gem-quality cubic ZrO2 exists. Produced by the skull-melt process. Key differences from diamond: SG 5.6–6.0 (much heavier than diamond at 3.52), RI 2.15–2.18 (off refractometer scale), higher dispersion than diamond. Coated CZ (TiN or other thin-film) simulates padparadscha, mystic topaz, or color-change effects; coating scratches easily — check girdle and culet under loupe. SG is the fastest single field separation test.

Cubic Zirconia has a specific gravity of 5.80 and a refractive index of 2.150–2.180, with a Mohs hardness of 8.0–8.5. It is singly refractive.

Physical & Optical Properties

RI Range2.150–2.180
SG Range5.60–6.00
SG Typical5.80
Hardness (Mohs)8–8.5
Crystal SystemCubic
Optic CharacterSR (Singly Refractive)
Dispersion0.066
Fluorescence LWInert
Fluorescence SWInert
Chelsea FilterInert
PleochroismNone
ColorsColorless, Red Pink, Blue Violet, Green, Yellow Orange, Brown, Purple, Black
SpeciesMan-made
ColorlessRed PinkBlue VioletGreenYellow OrangeBrownPurpleBlack

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

Cubic Zirconia no reading — over the limit 1.40 1.45 1.50 1.55 1.60 1.65 1.70 1.75 1.80 REFRACTIVE INDEX DORead the scale from bottom to top, then look for theliquid’s own faint line near the top. SEEThe field stays dark, with one faint line near 1.81 thatdoes not move when you change stones. MEANSOver the limit — this stone’s index is above the contactliquid’s own, so the liquid is the last thing the instrumentcan still see. That faint line is your proof the instrumentis working rather than dead. It is a RESULT: it eliminatesevery species below 1.81 in one observation. A field darkwith NO line means something else has gone wrong. 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

Cubic Zirconia Dark throughout (SR) 0° 45° 90° 135° ROTATION BETWEEN CROSSED POLARS Cubic Zirconia 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

Cubic Zirconia SG 5.60–6.00 WHERE IT SITS, AND WHAT ELSE IS THERE 1.0 2.0 3.0 4.0 5.0 SCALE ENDS AT 5.0 — THIS BAND RUNS PAST IT 1 other species in the table overlap this range, so a reading here narrows the field to 2 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

Cubic Zirconia One colour (no pleochroism) IDENTICAL AT EVERY ANGLE Cubic Zirconia shows no pleochroism, so both windows match at every orientation — turning the instrument changes nothing. That is a real negative result, and the reason it is worth knowing is below. 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 cubic zirconia is commercially available (Skull melting (cold-crucible RF induction — Zefyros/Ceres process)). Distinguishing natural from synthetic typically requires microscopic examination of internal features.

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

Common Simulants

Commonly Confused With

Commonly confused with: Diamond, White Sapphire, Topaz, Zircon.

Treatments

Related Comparisons

Diamond Vs Cubic Zirconia

Measurement Guides

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

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

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Studying for the GIA, FGA, or FEEG practical? Cubic Zirconia 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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