COMPARE GUIDE
Black SpinelVSBlack Tourmaline (Schorl)
Side-by-side comparison of physical properties, fluorescence, and crystal system — to identify by observation.
- ◎ is higher in Black Spinel, giving a numerical distinguishing point.
- ◎ is higher in Black Spinel, giving a numerical distinguishing point.
- ◎ is higher in Black 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: Black Spinel | B: Black Tourmaline (Schorl) | Verdict |
|---|---|---|---|
| Refractive index (RI) | 1.712–1.736 | 1.625–1.650 | A higher |
| Specific gravity (SG) | 3.58–3.90 | 3.10–3.20 | A higher |
| Mohs hardness | 8.0 | 7.0–7.5 | A higher |
| Birefringence | — | 0.020 | — |
| Dispersion | — | — | — |
| Property | A: Black Spinel | B: Black Tourmaline (Schorl) |
|---|---|---|
| Crystal system | 等軸晶系 | 三方晶系 |
| Pleochroism | — | — |
| Chelsea filter | — | inert |
| UV (long-wave) | — | inert |
| UV (short-wave) | inert | inert |
◆Black tourmaline (schorl Na(Fe²⁺₃)Al₆(Si₆O₁₈)(BO₃)₃(OH)₄, Mohs 7, SG 3.06, RI 1.624–1.658, doubly refractive uniaxial negative, characteristic vertical striations and columnar prismatic crystal form, opaque deep black with sub-vitreous lustre) versus black spinel (Mohs 8, SG 3.58–3.90, RI 1.712–1.736, singly refractive isotropic cubic, no striations, octahedral or massive crystal form, opaque deep black with sub-adamantine lustre). The vertical-striation test is unambiguous: black tourmaline shows characteristic deep vertical striations on prism faces while black spinel shows clean polished surfaces without striation. The hardness difference (Mohs 7 versus 8) is decisive on a scratch test. The specific-gravity difference (3.06 versus 3.58–3.90) is clean on hydrostatic balance. The lustre difference (sub-vitreous tourmaline versus sub-adamantine spinel) is visible to the trained eye. Black tourmaline trades at $5–$50 per carat versus black spinel at $5–$80 per carat — comparable pricing.
Distinguishing tools
Tools that decide between Black Spinel and Black Tourmaline (Schorl) 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.