← Back to Reference Database RI Chart SG Chart Fluorescence Hardness

Synthetic Spinel

Last updated: April 2026

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.

Physical & Optical Properties

RI Range1.725–1.728

SG Range3.52–3.65

SG Typical3.61

Hardness (Mohs)8

Crystal SystemCubic

Optic CharacterSR (Singly Refractive)

Dispersion0.020

Fluorescence LWStrong Blue White

Fluorescence SWStrong Blue White

Chelsea FilterRed

PleochroismNone

ColorsBlue Violet, Red Pink, Colorless, Green, Yellow Orange

SpeciesSpinel (synthetic)

VarietyFlame Fusion (Verneuil)

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)

GemID Pro includes a two-phase natural vs. synthetic testing protocol for Synthetic Spinel.

Start Free Trial

Commonly Confused With

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

Price Context

Natural — low ($/ct)$1

Natural — high ($/ct)$20

NotePer carat; mass-produced synthetic, low value

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

Measurement Guides

Identifying a synthetic spinel? GemID walks through these tests in order — RI, SG, fluorescence, and more.

Try GemID Free →