Gem Comparisons & Identification Guides

Protocols and comparisons for difficult identification decisions — when two candidates share similar RI and you need additional tests to separate them.

Guides

App Comparison

GemID vs. AI Photo Apps

Why measured properties — RI, SG, fluorescence — identify gems more reliably than visual pattern recognition. Includes feature comparison table.

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Complete Workflow

How to Identify an Unknown Gemstone

The complete step-by-step workflow. Start here if you have an unknown stone and want a structured approach.

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Protocol

Natural vs. Synthetic Testing

Two-phase protocol covering 33 species with known synthetics — from corundum to emerald to alexandrite.

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Gem Comparisons

Colorless Stones

Diamond vs Moissanite

Thermal testers fail — both read "diamond." Facet doubling under 10x and electrical conductivity testing are the definitive separators.

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Colorless Stones

Diamond vs Cubic Zirconia

CZ reads "simulant" on thermal testers and has dramatically higher SG (5.60-6.00 vs 3.50-3.53). The easiest diamond simulant to detect.

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Red Stones

Ruby vs Red Spinel

Ruby is DR with RI 1.762-1.770; spinel is SR with RI 1.712-1.736. Polariscope and dichroscope separate them in seconds.

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Red Stones

Ruby vs Garnet

Pyrope and almandine garnet mimic ruby's color. The polariscope is definitive: ruby blinks (DR), garnets stay dark (SR).

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Green Stones

Emerald vs Tsavorite

Both show Chelsea red (chromium coloring), but RI separates them cleanly: emerald 1.565-1.602, tsavorite 1.730-1.760. No overlap.

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Blue Stones

Sapphire vs Tanzanite

RI gap of 0.06+ is definitive. Tanzanite's strong trichroism (blue/violet/burgundy) is the fastest visual separator.

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Jade

Jadeite vs Nephrite

Both are "jade" but different minerals. SG is the most practical test: jadeite 3.24-3.43, nephrite 2.90-3.03 — no overlap.

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Color-Change Stones

Alexandrite vs Color-Change Garnet

RI and SG overlap — but the polariscope is definitive. Alexandrite blinks (DR biaxial), garnet stays dark (SR isotropic).

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Natural vs Synthetic

Natural vs Synthetic Ruby

Identical RI, SG, and hardness. Curved striae (Verneuil), flux veils, or chevron growth patterns under magnification are the key separators.

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Natural vs Synthetic

Natural vs Synthetic Emerald

Similar RI and SG make this challenging. Three-phase inclusions (natural) vs flux veils or chevron growth (synthetic) under magnification provide the answer.

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Browse the reference database for full property tables on all 130 gem species.

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