Synthetic Spinel

Key Differentiators

• Strong 'tabby extinction' (checkerboard-like ADR) on polariscope — diagnostic for synthetic origin
• Cobalt-blue variety: vivid red through Chelsea filter — immediately diagnostic
• RI 1.725–1.728 — slightly elevated vs natural spinel (1.712–1.730)
• Dominant simulant in 1940s–1980s estate jewelry
• Unusually clean under loupe — lack of natural inclusions

Natural vs. Synthetic

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

• Polariscope: Natural spinel: may show mild ADR but typically more uniform extinction Synthetic: Synthetic: very strong tabby (checkerboard-like) anomalous extinction — diagnostically useful
• Chelsea Filter (cobalt-blue varieties): Natural blue spinel: varies; may show weak red response Synthetic: Synthetic cobalt-blue: vivid strong red — conclusive indicator of cobalt coloring
• Refractometer: Natural spinel: typically 1.712–1.730 Synthetic: Synthetic flame-fusion: 1.725–1.728 (elevated due to excess alumina)

Commonly Confused With

Commonly confused with: Sapphire, Ruby, Aquamarine, Emerald, Peridot, Alexandrite.

Price Context

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

About Synthetic Spinel

Flame-fusion synthetic spinel was the dominant birthstone simulant from the 1930s–1980s. Estate jewelry from this era frequently contains it as a simulant for sapphire, aquamarine, ruby, and alexandrite. The cobalt-blue variety shows a strong red Chelsea filter reaction. All varieties show anomalous double refraction ('tabby extinction') on the polariscope. RI is slightly elevated vs. natural spinel due to excess alumina in the Verneuil process.