Gem Comparisons & Identification Guides

Last updated: August 2026

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

Guides

App Comparison

Loupewise 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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Instrument Comparison

Dichroscope vs. Polariscope

Which one first? Both measured against all 132 species — what each decides, the trap each sets, and why they are better together.

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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 41 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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Colorless Stones

White Sapphire vs Diamond

The natural colorless simulant. RI separates them: white sapphire reads 1.762-1.770; diamond is over the refractometer limit. Dispersion 0.018 vs 0.044 — the fire gives it away.

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Colorless Stones

Zircon vs Diamond

Both adamantine with strong fire, but zircon's extreme facet doubling gives it away in seconds under a 10x loupe. SG separates them too: 4.60-4.80 vs 3.50-3.53.

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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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Red Stones

Pink Sapphire vs Ruby

Both are corundum with identical RI, SG, and hardness — no instrument separates them. The name is a color-saturation call, not a measurement.

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Red Stones

Pyrope Garnet vs Spinel

Both singly refractive, with overlapping RI and SG. The spectroscope and UV fluorescence separate this classic exam pair.

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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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Green Stones

Peridot vs Sinhalite

Overlapping RI and visible doubling in both make this a genuine exam trap. Sinhalite's diagnostic 452/475/493 nm absorption bands decide it.

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Blue-Green Stones

Paraiba Tourmaline vs Apatite

Neon blue-green apatite is the classic Paraiba look-alike. Birefringence (0.018 vs 0.006), SG, and hardness make the separation; copper confirmation needs a lab.

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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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Blue Stones

Aquamarine vs Blue Topaz

The most common commercial mix-up in blue gems. SG (2.68-2.78 vs 3.49-3.57) and RI separate them cleanly — topaz is far denser and reads higher.

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Blue Stones

Tanzanite vs Iolite

The budget-substitute confusion. Both are strongly trichroic, but RI (1.691-1.700 vs 1.540-1.560) and SG clearly separate them.

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Violet Stones

Amethyst vs Iolite

Two violet stones whose RI and SG ranges overlap. Iolite's strong trichroism is the diagnostic test — the dichroscope separates them in seconds.

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Violet Stones

Amethyst vs Scapolite

Overlapping RI and SG make this a real exam separation. Optic sign (uniaxial + vs −) and scapolite's strong orange UV fluorescence decide it.

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Yellow Stones

Citrine vs Topaz

Two yellow gems that trade names constantly blur. SG is the fastest separator (2.63-2.65 vs 3.49-3.57 — the heft test works), and the RI ranges don't overlap.

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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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Jade

Jadeite vs Serpentine

Serpentine is the most common jade impostor, sold as "new jade" or "Korean jade". Hardness (6.5-7 vs 3-4) and SG separate them fast; RI confirms.

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Simulant Detection

Turquoise vs Howlite

Dyed howlite is the #1 turquoise imitation. SG, hardness, the acetone test, and turquoise's copper absorption band separate them.

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Simulant Detection

Quartz vs Glass

Scratch test, specific gravity, and loupe checks — round gas bubbles, swirl marks — separate real quartz from glass. The polariscope confirms: quartz is DR, glass SR.

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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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Natural vs Synthetic

Natural vs Synthetic Amethyst

Both are real quartz with identical RI, SG, and hardness. Tiger-stripe inclusions, Brazil-law twinning, color zoning, and FTIR separate them.

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Natural vs Synthetic

Natural vs Synthetic Spinel

Unlike most synthetics, flame-fusion spinel differs measurably: elevated RI (1.725-1.728), "tabby extinction" on the polariscope, and a red Chelsea reaction in cobalt blue.

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Treatment Detection

Smoky Quartz: Natural vs Irradiated

Natural smoky quartz is colored by natural irradiation — lab irradiation produces the same result. What can honestly be assessed, and what requires a laboratory.

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Browse the reference database for full property tables on all 132 gem species.

Reference Database →