Ruby

Real mineral · very rare · Al₂O₃

Red corundum coloured by chromium impurities. Forms in marble under high-grade metamorphic conditions. Star rubies display asterism caused by rutile needle inclusions oriented along the crystal axes.

Identity

Formula

Al₂O₃

Chemical class

oxide

Mineral group

Corundum, Sapphire

Also known as

Red corundum, Carbuncle (archaic)

Crystallography

Crystal system

trigonal

Habits

tabular, prismatic, rhombohedral

Fracture

conchoidal

Physical properties

Mohs hardness

9

Density

4 g/cm³

Luster

vitreous, adamantine

Colors

red, pink-red, orange-red, garnet-red

Streak

white

Transparency

transparent, translucent

Geology

Origins

metamorphic, igneous

Host rocks

marble, basalt, schist

Associated minerals

Spinel, Sapphire, Calcite, Tourmaline

Geography

Myanmar, Sri Lanka, Thailand, Mozambique, Afghanistan

Classification

Rarity

very rare

Gem quality

Yes

Arcane properties

Affinity

fire, life

Effects

elemental fire, healing

Planar origin

Material Plane

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