Corundum

Physical Properties
Chemical formula Al2O3
Class Oxide
Crystal system Hexagonal (rhombohedral)
Habit Hexagonal
Tabular
Prismatic
Massive
GranularEuhedral crystals are rare.
Color Brown
Blue
Pink
Red (ruby)
Green
Yellow
Multicolored
Hardness 9
Specific gravity 3.9 to 4.1
Cleavage None
Fracture Uneven
Rectangular parting
Luster Adamantine
Vitreous
Transparency Transparent to translucent
Streak White
Optical Properties
PPL Typically colorless
May be pale pink, blue, green,
or yellow
Extremely high relief
XPL 1st order greys/yellows
δ 0.008
after Perkins, 371-372

Corundum in Hand Sample

Corundum hand sample

Pinkish red corundum (ruby) with black hornblende in the epidote-family mineral zoisite

Corundum in Thin Section

Stay tuned!

Further Reading

Corundum at webmineral.com

Corundum at mindat.org