Black Spinel

Related: Spinel Varieties

Spinel

Key Differentiators

• Singly refractive
• Hardness of 8
• Vitreous luster

Natural vs. Synthetic

Synthetic black spinel is commercially available (Flame fusion (Verneuil)). Distinguishing natural from synthetic typically requires microscopic examination of internal features.

• RI: RI ~1.718–1.725 for natural black spinel. Synthetic: Flame fusion synthetic spinel RI ~1.727 — distinctly higher. Quick refractometer check is a useful indicator.
• Polariscope (ADR): Weak to moderate anomalous double refraction (ADR). Faint wavy or patchy extinction. Synthetic: Strong tabby extinction — checkerboard ADR pattern under crossed polarizers. Diagnostically useful for flame fusion.
• Microscopy: Natural inclusions: negative crystals (angular/hexagonal), irregular fluid inclusions, growth zoning. Synthetic: Curved growth striae and spherical/tadpole gas bubbles. Often in rows parallel to striae.

Common Simulants

• Black diamond: Diamond has extreme hardness (10 Mohs); thermal probe reacts strongly; RI much higher (~2.42); SG 3.52.
• Black onyx / chalcedony: Aggregate optic character; RI 1.530–1.540; SG ~2.65; much lower hardness (6.5–7 Mohs).

Commonly Confused With

Commonly confused with: Black Diamond, Black Onyx, Black Tourmaline Schorl.

Treatments

• Surface Coating (to enhance luster or color)
• Fracture Filling (resin/glass)

Price Context

Price context is approximate. GemID is not an appraisal tool. Results are indicators, not certified valuations.

Measurement Guides

How to Identify a GemstoneHow to Measure Specific GravityHow to Use a RefractometerUV Fluorescence Testing