Sapphire

Sapphire
The 423-carat (85 g) blue Logan sapphire
General
Category	Oxide mineral
Formula (repeatin unit)	aluminium oxide, Al2O3
Creestal seestem	Trigonal Seembol (32/m) Space Group: R3c
Identification
Colour	Often Blue but varies
Creestal habit	massive an granular
Cleavage	none
Fractur	conchoidal, splintery
Mohs scale haurdness	9.0
Skinkle	vitreous
Streak	white
Speceefic gravity	3.95–4.03
Optical properties	Abbe nummer 72.2
Refractive index	nω=1.768–1.772 nε=1.760–1.763, Birefringence 0.008
Pleochroism	Strang
Meltin pynt	2030–2050 °C
Fusibility	infusible
Solubility	Insoluble
Ither chairacteristics	coefficient o thermal expansion (5.0–6.6)×10−6/K

Sapphire (Greek: σάπφειρος; sappheiros, 'blue stane', which probably referred insteid at the time tae lapis lazuli) is a gemstane variety o the mineral corundum, an aluminium oxide (α-Al₂O₃). Trace amoonts o ither elements sic as airn, titanium, chromium, copper, or magnesium can gie corundum blue, yellae, purpie, orange, or a greenish colour. Chromium impurities in corundum yield a pink or reid tint, the latter bein cried a ruby.