Sapphire

Crystal system · Trigonal

Identity

Formula

Al2O3

IMA symbol

Crn

Strunz class

4.CB

Crystal system

Trigonal

Point group

-3m

Variety of

Corundum

Type locality

(gem variety of corundum), Sri Lanka

Physical properties12 recorded

Hardness

9 (Mohs)

Specific gravity

3.97–4.05

Refractive index

1.762–1.778

Birefringence

0.008

Dispersion

0.018

Optic character

uniaxial (−)

Luster

vitreous / adamantine

Diaphaneity

transparent-to-translucent

Tenacity

brittle to tough

Cleavage

none · — (parting on basal)

Fracture

conchoidal

Magnetism

weakly paramagnetic · Very slight (Fe/Ti)

Treatment & disclosurebuyer information

Heat treatmentuniversalstable

Same as ruby — silk-dissolution and color improvement standard since ancient times.

Detection: moderate

Beryllium diffusioncommonstable

Lattice diffusion of Be creates orange-pink "padparadscha" colors. Requires advanced testing to detect.

Detection: hard

Titanium diffusionoccasionalstable-care

Surface-only blue color — repolishing removes the color. Disclosure required.

Detection: moderate

Notable localities3

MogokMyanmar · Mandalay Region
Mogok ValleyMyanmar · Mandalay
RatnapuraSri Lanka · Sabaragamuwa