Ruby

Related: Corundum Varieties

Color-Change SapphirePadparadscha SapphirePink SapphireSapphireStar RubyStar SapphireWhite SapphireYellow Sapphire

Key Differentiators

• Strong red fluorescence (LW)
• Strong dichroism
• Hardness of 9
• Hexagonal growth lines

Natural vs. Synthetic

Synthetic ruby is commercially available (Flame fusion (Verneuil), Flux (Chatham, Ramaura, Kashan), Hydrothermal, and others). Distinguishing natural from synthetic typically requires microscopic examination of internal features.

• Microscopy — inclusions: Natural ruby: rutile silk (fine needles crossing at 60°/120°), angular growth zoning (hexagonal), fingerprint healing fractures, zircon crystals with stress halos, apatite crystals, platelets. Inclusions presence is a positive sign. Synthetic: Flame fusion: curved growth striae (diagnostic), spherical/tadpole gas bubbles, wavy extinction on polariscope. Flux: wispy/glassy flux veils, platinum platelets (metallic, reflective), angular growth. Hydrothermal: nail-head spicules/chevron growth, seed crystal, straight parallel growth lines. Czochralski: often very clean, platinum particles if any, extremely strong red UV fluorescence.
• UV Fluorescence: Natural ruby: moderate to strong red LW UV. May be quenched by iron in some origins (Thai/Cambodian rubies are near-inert). Mosambique/Burmese show strong fluorescence. Synthetic: Flame fusion: very strong, often chalky red, SW can equal or exceed LW. Czochralski: extremely intense, near-blinding red fluorescence. Too-strong SW fluorescence compared to LW is suspicious.
• Chelsea Filter: Natural ruby: moderate to strong red. Variable with iron content (iron-rich = weaker). Synthetic: Flame fusion / flux: strong to very strong red due to high Cr, low Fe. Alone not diagnostic (fine natural rubies also react strongly).
• Polariscope (ADR): Patchy or wavy extinction from natural twinning and growth strain. Synthetic: Flame fusion: strong, pronounced wavy/anomalous extinction — highly characteristic.

Common Simulants

• Red Spinel: Isotropic (SR) — no facet doubling; no trichroism under dichroscope; different fluorescence character.
• Red tourmaline (rubellite): Uniaxial negative DR; strong dichroism (red/orange-red); RI 1.624–1.644; SG 3.06; lower hardness (7–7.5 Mohs).
• Red garnet (pyrope/almandine): Isotropic (SR); typically inert under UV; RI 1.720–1.790; no fluorescence; Chelsea filter inert.
• Red Glass: Isotropic; gas bubbles and/or swirl marks under loupe; conchoidal fracture; lower SG.

Commonly Confused With

Commonly confused with: Spinel, Tourmaline, garnet, glass, Almandine Garnet, Pyrope Garnet, Rhodolite Garnet, Rubellite, Synthetic Spinel, YAG.

Treatments

• Low-Temperature Heat (< 1200°C)
• High-Temperature Heat (> 1400°C)
• Lead Glass Fracture Filling
• Flux Healing of Fractures
• Beryllium Diffusion (Lattice Diffusion)

Price Context

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

About Ruby

Ruby is the red variety of corundum. Origin affects value and fluorescence: Burmese (Mogok) rubies have low iron and show strong red LW fluorescence; Thai/Cambodian rubies have higher iron and weaker fluorescence; Mozambique rubies (Montepuez) show strong fluorescence similar to Burmese. Origin determination requires lab analysis (EDXRF, UV-Vis spectrum).