COMPARE GUIDE
Gray MoonstoneVSGray Spinel
Side-by-side comparison of physical properties, fluorescence, and crystal system — to identify by observation.
- ◎ is higher in Gray Spinel, giving a numerical distinguishing point.
- ◎ is higher in Gray Spinel, giving a numerical distinguishing point.
- ◎ is higher in Gray Spinel, giving a numerical distinguishing point.
Note: properties whose numeric ranges do not overlap are auto-extracted. Both are measurable with a refractometer or heavy-liquid bath.
| Property | A: Gray Moonstone | B: Gray Spinel | Verdict |
|---|---|---|---|
| Refractive index (RI) | 1.518–1.526 | 1.712–1.736 | B higher |
| Specific gravity (SG) | 2.55–2.61 | 3.58–3.61 | B higher |
| Mohs hardness | 6.0–6.5 | 8.0 | B higher |
| Birefringence | 0.005 | — | — |
| Dispersion | — | — | — |
| Property | A: Gray Moonstone | B: Gray Spinel |
|---|---|---|
| Crystal system | 単斜晶系 | 等軸晶系 |
| Pleochroism | — | — |
| Chelsea filter | — | — |
| UV (long-wave) | — | — |
| UV (short-wave) | weak (orange) | inert |
◆Grey moonstone (orthoclase feldspar K(AlSi₃O₈), Mohs 6, SG 2.55–2.58, RI 1.518–1.526, doubly refractive biaxial negative, characteristic billowing adularescence 'moonstone sheen,' typically translucent to semi-transparent) versus grey spinel (Mohs 8, SG 3.58–3.61, RI 1.712–1.736, singly refractive isotropic cubic, no adularescence, transparent). The adularescence test is unambiguous: grey moonstone shows the characteristic billowing soft-glow sheen from internal albite-orthoclase lamellae while grey spinel shows transparent crystalline lustre without sheen. The specific-gravity difference (2.55–2.58 versus 3.58–3.61) and refractive-index difference (1.518–1.526 versus 1.712–1.736) are dramatic and diagnostic. The hardness difference (Mohs 6 versus 8) is decisive on scratch tests.
Distinguishing tools
Tools that decide between Gray Moonstone and Gray Spinel 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.