Ruby

Ruby
Naitural ruby crystals frae Winza, Tanzanie
General
Category	Mineral variety
Formula (repeatin unit)	aluminium oxide wi chromium, Al2O3:Cr
Creestal seestem	Trigonal (Hexagonal Scalenohedral), symbol (−3 2/m), space group R3c
Identification
Colour	Reid, mey be brounish, purplish, or pinkish
Creestal habit	Varies wi locality. Terminated tabular hexagonal prisms.
Cleavage	Na true cleavage
Fractur	Uneven or conchoidal
Mohs scale haurdness	9.0
Skinkle	Vitreous
Streak	white
Diaphaneity	transparent
Speceefic gravity	4.0
Refractive index	nω=1.768–1.772 nε=1.760–1.763
Birefringence	0.008
Pleochroism	Orangey reid, purplish reid
Ultraviolet fluorescence	reid unner longwave
Meltin pynt	2044 °C
Solubility	none
Major varieties
Sapphire	Ony color except shades o reid
Corundum	various colors
Emery	Granular

A ruby is a pink tae bluid-reid coloured gemstane, a variety o the mineral corundum (aluminium oxide). The reid colour is caused mainly bi the presence o the element chromium. Its name comes frae ruber, Laitin for reid. Ither varieties o gem-quality corundum are cried sapphires. The ruby is considered ane o the fower precious stanes, thegither wi the sapphire, the emerald, an the diamond.

Prices o rubies are primarily determined bi colour. The brichtest an maist valuable "reid" cried bluid-red, commands a lairge premium ower ither rubies o seemilar quality. Efter colour follaes clarity: seemilar tae diamonds, a clear stane will command a premium, but a ruby wioot ony needle-lik rutile inclusions mey indicate that the stane haes been treatit. Cut an carat (wicht) are an aa an important factor in determinin the price.