Ruby
Chemical Formula	Al2O3:Cr
Species	Oxides & Hydroxides
Crystal System	Trigonal
Mohs Scale	9
Specific Gravity	4.0
Color	Red, may be brownish, purplish or pinkish
Streak	white
Luster	Vitreous
Refractive Index	nω=1.768–1.772nε=1.760–1.763
Diaphaneity	transparent
Cleavage	No true cleavage
Fracture	Uneven or conchoidal
Crystal Habit：Varies with locality. Terminated tabular hexagonal prisms.