COMPARE GUIDE
Black OpalVSAssembled Opal (Doublet / Triplet)
Side-by-side comparison of physical properties, fluorescence, and crystal system — to identify by observation.
Physical propertiesPROPERTIES
| Property | A: Black Opal | B: Assembled Opal (Doublet / Triplet) | Verdict |
|---|---|---|---|
| Refractive index (RI) | 1.430–1.470 | 1.440–1.470 | Overlap |
| Specific gravity (SG) | 1.97–2.20 | 2.00–2.50 | Overlap |
| Mohs hardness | 5.5–6.5 | 5.5–6.0 | Overlap |
| Birefringence | — | — | — |
| Dispersion | — | — | — |
Optics & fluorescenceOPTICS & UV
| Property | A: Black Opal | B: Assembled Opal (Doublet / Triplet) |
|---|---|---|
| Crystal system | 非晶質（含水シリカ） | 非晶質（貼り合わせ） |
| Pleochroism | — | — |
| Chelsea filter | inert | — |
| UV (long-wave) | weak (green / blue) | — |
| UV (short-wave) | inert | weak (white) |
ObservationOBSERVATION
◆Doublets and triplets show a visible glue line when viewed from the side at the girdle. A solid opal has a smooth, continuous profile.
Color categoriesCATEGORIES
A: Black Opal
Opal
B: Assembled Opal (Doublet / Triplet)
Opal
DISTINGUISHING TOOLS · 2 ITEMS
Distinguishing tools
Tools that decide between Black Opal and Assembled Opal (Doublet / Triplet) 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.