Sapphires

 
Color : Blue in various hues, colorless, pink, orange, yellow, green, purple, black  
Color of streak: White

Mohs’ hardness : 9
Specific gravity : 3.99-4.00   
Cleavage : None 

Fracture: Small conchoidal, uneven, splintery 
Crystal system : Trigonal
Chemical composition : Aluminium oxide
Refractive index : 1.766-1.774
Double refraction : -0.008
Fluorescence : Blues ; (purple) none Yellows from Sri Lanka : weak ; orange ; colorless : orange-yellow or purple  


The name sapphire (Greek – blue) used to be applied to various stones. In antiquity and as late as the Middle Ages, the name sapphire was understood to mean what is today described as lapis lazuli. Around 1800 it was recognized that sapphire and ruby are gem varieties of corundum. At first only the blue variety was called sapphire, the corundums of other colors (with the exception of red) were given special, misleading names, such as “Oriental peridot” for the green variety or “Oriental topaz” for the yellow type. Today corundums of all colors except red are called sapphires. Red varieties are called rubies. The various colors of sapphire are qualified by description, ie. Yellow sapphire, green sapphire. Sapphire without additional qualification refers to blue corundum. Orange pink sapphire is called Padparadchah (Sinhalese for  “Lotus Flower”).