COMPARE GUIDE
Fire OpalVSMexican Opal
Side-by-side comparison of physical properties, fluorescence, and crystal system — to identify by observation.
Physical propertiesPROPERTIES
| Property | A: Fire Opal | B: Mexican Opal | Verdict |
|---|---|---|---|
| Refractive index (RI) | 1.430–1.460 | 1.430–1.460 | Nearly equal |
| Specific gravity (SG) | 2.00–2.20 | 1.97–2.20 | Overlap |
| Mohs hardness | 5.5–6.5 | 5.5–6.5 | Nearly equal |
| Birefringence | — | — | — |
| Dispersion | — | — | — |
Optics & fluorescenceOPTICS & UV
| Property | A: Fire Opal | B: Mexican Opal |
|---|---|---|
| Crystal system | 非晶質（含水シリカ） | 非晶質（含水シリカ） |
| Pleochroism | — | — |
| Chelsea filter | inert | — |
| UV (long-wave) | weak (green) | — |
| UV (short-wave) | weak (green) | weak (green) |
ObservationOBSERVATION
◆'Fire opal' and 'Mexican opal' overlap heavily — the trade often uses them interchangeably for the orange-red Mexican material. Mexican opal is the geographic term; fire opal is the body-color category.
Color categoriesCATEGORIES
A: Fire Opal
Opal / Yellow / orange
B: Mexican Opal
Opal
DISTINGUISHING TOOLS · 2 ITEMS
Distinguishing tools
Tools that decide between Fire Opal and Mexican Opal in practice.
Note: this page is auto-generated from published GIA / CGL reference values. Individual stones, treatments, and synthetics may fall outside these ranges. For a definitive identification, consult an accredited gem laboratory.