GEMSTONE FIELD GUIDE
Zircon
Mineral, crystalline to structurally radiation-damaged. High, medium and low types describe structural/property states, not quality grades
Blue round brilliant-cut zircon, NMNH G10660-00, in the Smithsonian National Gem Collection.
Facets and internal reflections create this blue zircon's bright appearance. Color in a photograph is not a calibrated standard or a treatment test.
Greg Polley / Smithsonian National Museum of Natural History, NMNH G10660-00 / CC0 · Source ↗ · CC0 1.0 Universal · resized for the webA verified 3D specimen capture is not available for this entry. No generated stand-in is used.
AT A GLANCE
Start with the evidence.
Zircon is not cubic zirconia. Ordinary high zircon retains an ordered crystal structure; intermediate zircon is partly damaged, and low (metamict) zircon has extensive radiation-related structural disruption. Their optical properties need not match.
- Gem-A — Understanding Zircon (2022) ↗
- GIA — Zircon description and structural types ↗
- GIA — Chemical Analysis of Zircon (2015), structural categories ↗
- Refractive index (RI)
- High: 1.925–1.984 (±0.040); medium: 1.875–1.905 (±0.030); low: 1.810–1.815 (±0.030)
- Specific gravity (SG)
- 3.90–4.73
- Mohs hardness
- 6–7.5 (low to high)
GIA structural-type reference ranges
How to read this value
These ranges are above a common 1.78-contact-liquid refractometer setup; an over-the-limit result is not a numeric measurement and is not by itself diagnostic. A high-type crystal's double refraction must not be required of low/metamict zircon.
GIA broad zircon reference
How to read this value
Structural state is material to interpretation; do not use one fixed zircon SG.
GIA structural-type reference
These are reference properties, not measurements of the pictured specimen. Reference images are educational—not NumisTrends sale inventory.
See the details and limitations ↓01 · IDENTIFY
Build a profile, not a guess.
Natural zircon, not cubic zirconia. Structural damage changes optical properties, density and hardness; do not flatten the three types into one fixed value.
Refractive index (RI)High: 1.925–1.984 (±0.040); medium: 1.875–1.905 (±0.030); low: 1.810–1.815 (±0.030)
GIA structural-type reference ranges
These ranges are above a common 1.78-contact-liquid refractometer setup; an over-the-limit result is not a numeric measurement and is not by itself diagnostic. A high-type crystal's double refraction must not be required of low/metamict zircon.
Specific gravity (SG)3.90–4.73
GIA broad zircon reference
Structural state is material to interpretation; do not use one fixed zircon SG.
Mohs hardness6–7.5 (low to high)
GIA structural-type reference
Birefringence0.000–0.059 (low to high)
GIA low-to-high structural types
Optic characterUniaxial (+) when crystalline; may be isotropic when metamict
Structural-state dependent
CleavageIndistinct on {110} and {111}
MSA crystalline-mineral reference
Open a property for its scope and source. RI and specific gravity have no units. Mohs describes scratch resistance—not resistance to breaking. Do not scratch a stone to test it.
What can look similar?
Cubic zirconia (CZ)
The similar names obscure two different materials; CZ is not laboratory-grown zircon.
How to investigate. A gemologist compares optical character and other properties. CZ is singly refractive.
Lack of visible doubling alone cannot exclude low zircon.
Diamond
Colorless zircon's brilliance and fire can resemble diamond.
How to investigate. Professional optical examination matters: true double refraction is inconsistent with diamond.
Sparkle alone identifies neither material; other diamond simulants can also show doubling.
02 · TESTS & ULTRAVIOLET
What a test can—and cannot—tell you.
Results depend on the specimen, instrument and method. This is a reference for understanding evidence, not a home authentication or treatment verdict.
UV reaction
- Long-wave UV
- GIA's 2021 color-change case, a 4.60 ct zircon, showed no longwave fluorescence.
- Short-wave UV
- That specimen showed weak yellow shortwave fluorescence.
Case-specific, not diagnostic. Some zircon colors can change under UV; do not use UV as a home identification test. Let a laboratory choose suitable examination methods.
Optic character and facet-image inspection
Whether optical behavior supports zircon.
Reference observation. Many zircons show conspicuous doubling of facet edges.
Limit. Structural damage in low zircon can reduce or eliminate doubling; its absence does not exclude zircon.
Absorption-spectrum assessment
Whether the absorption pattern supports zircon.
Reference observation. Many zircons show a recognizable red-region band.
Limit. Some zircons show no useful spectrum, and rare other minerals can resemble it; unresolved cases need additional tests.
Real laboratory examples
Documented cases, not test results of the reference specimens shown on this page.
Lighting changed a zircon's apparent color
GIA's 4.60 ct zircon appeared grayish purple under cool LED light but green under a cool fluorescent lamp. Its absorption interacted differently with the two light sources.
The takeaway. Record the lighting when comparing color; an apparent mismatch is not, by itself, evidence that two descriptions concern different stones.
Use a qualified gemologist for identification work. Do not expose eyes or skin to UV sources, or perform scratch, heat, acid or solvent tests on a gemstone. Do not assume that an absent UV reaction rules a material out.
03 · TREATMENTS & CARE
Protect the stone you actually have.
Disclosed treatments, fractures and settings can change which cleaning methods are appropriate.
Use warm soapy water, not ultrasonic or steam cleaning. Protect facet edges from knocks and rubbing; heat can change color, and some heat-treated zircon can change after prolonged bright-light exposure.
04 · SOURCES & SCOPE
Know where each fact comes from.
Original NumisTrends explanations with primary references. This is not a replacement for gemological training, a laboratory report, or the examination of your own stone.
Properties reviewed: 2026-09-07 · Identification notes reviewed: 2026-09-07
- GIA — Zircon ↗
- MSA Handbook of Mineralogy — Zircon ↗
- GIA — Zircon Care and Cleaning ↗
- Gem-A — Refractometer specification (1.78 contact liquid) ↗
Supporting reference verified from the official search excerpt; full document not reviewed.
NumisTrends is independent of GIA, Gem-A and the museums cited. A matching property cannot by itself establish identity, natural versus laboratory-grown origin, treatment, geographic origin, grade or value.