Sapphire

← Back to Reference Database RI Chart SG Chart Fluorescence Hardness

Physical & Optical Properties

RI Range1.762–1.770

SG Range3.95–4.03

SG Typical4.00

Hardness (Mohs)9

Crystal SystemTrigonal

Optic CharacterDR Uniaxial (−)

Birefringence0.008

Dispersion0.018

Fluorescence LWVariable

Fluorescence SWInert

Chelsea FilterVariable

PleochroismStrong Dichroic

ColorsBlue Violet, Red Pink, Yellow Orange, Green, Colorless, Purple, Black, Color Change

SpeciesCorundum

Key Differentiators

Strong dichroism
Hardness of 9
Hexagonal color zoning
Silk inclusions
Chelsea filter: variable — blue sapphire typically inert; pink/yellow/padparadscha may show orange-pink

Natural vs. Synthetic

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

Microscopy — inclusions: Natural sapphire: rutile silk, zircon crystals with halos, growth zoning (angular/hexagonal), fingerprint healing fractures, liquid inclusions, apatite/columbite crystals. Synthetic: Same as ruby entry above. Flame fusion: curved growth striae and gas bubbles (diagnostic). Flux: flux veils and platinum. Hydrothermal: nail-head spicules, seed plate. Czochralski: typically very clean.
Spectroscope (blue sapphire): Natural blue sapphire: iron absorption lines at 450nm, 460nm, 471nm typically present — confirm with handheld spectroscope. Synthetic: All synthetic methods: iron lines weak or absent (unless intentionally doped). Near-absence of 450/460nm iron lines in blue sapphire is suspicious for synthetic.
UV Fluorescence (blue sapphire): Natural blue sapphire: typically inert to weak orange-red. Iron quenches fluorescence in most natural material. Synthetic: Synthetic blue sapphire: generally inert to weak — very similar to natural. Not strongly diagnostic for blue sapphire. Flame fusion yellow sapphire often shows strong orange-yellow LW fluorescence.
Heat treatment note: Most commercial sapphires are heat-treated to improve color and clarity. Unheated stones command premium. Standard gemological tools cannot reliably detect heat treatment — requires lab (FTIR, UV-Vis). Synthetic: N/A

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

Start Free Trial

Common Simulants

Blue spinel: Isotropic (SR) — no trichroism; no facet doubling; RI ~1.718; SG ~3.60.
Tanzanite: Biaxial positive DR; very strong trichroism (blue-violet-burgundy red); SG 3.35; softer (6.5 Mohs); lower RI (1.691–1.700).
Iolite: Biaxial negative DR; pronounced trichroism (blue-gray-pale yellow); low SG (2.58–2.66); RI 1.542–1.551; much softer (7–7.5 Mohs).
Blue tourmaline (indicolite): Uniaxial negative DR; dichroic (blue/blue-green); RI 1.624–1.644; SG 3.06.
Blue Glass: Isotropic; gas bubbles or swirl marks; no dichroism; conchoidal fracture; SG varies.

Commonly Confused With

Commonly confused with: Spinel, Tanzanite, Iolite, Tourmaline, Glass, Chrysoberyl, Indicolite, Synthetic Spinel, Topaz, YAG, Zircon.

Treatments

Heat Treatment
Beryllium (Lattice) Diffusion
Irradiation
Glass/Resin Fracture Filling
Surface Diffusion (Ti/Fe — historical)

Price Context

Natural — low ($/ct)$1,000

Natural — high ($/ct)$15,000

NotePer carat; Kashmir and Burmese unheated blue command top premiums; GIA/AGL origin reports add value

Synthetic — low ($/ct)$5

Synthetic — high ($/ct)$50

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

Related Comparisons

Measurement Guides

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

Try GemID Free →