Sapphire is one of the top four in popularity of gems; Diamond, Sapphire, Ruby, and Emerald. This is mostly due to its beauty, variety of colors and toughness as a jewelry gem. It is typically thought of as being a blue gem, but it is available in many other colors including blue-green, green, violet, purple, orange, yellow, golden, peachy pink, pink, colorless, and black. Ruby is the red or the pinkish red variety of Corundum. With a Moh’s hardness of 9.0 and no cleavage, it is a very durable gem for jewelry.
Sapphire is available from many locations around the world. Some of these locations, like Cambodia, Ceylon, and Kashmir, are well known for their fine Sapphires.
|Crystallography:||Trigonal – Hexagonal Scalenohedral|
|Crystal Habit:||Crystals hexagonal, prismatic or steeply dipyramidal, tabular, rhombohedral, rarely acicular, typically rough, to 1 m; sectorially striated on  k . Also granular, massive.|
|Twinning:||Common lamellar k , may be an exsolution phenomenon. Contact or penetration twins on  or , rare.|
|Cleavage:||None; Partings on  and |
|Density:||3.99 – 4.10 (g/cm3)|
|Color:||Colorless, Gray, Brown, Pink, Orange, Yellow, Green, Blue to Cornflower Blue, Violet; may be color zoned, asteriated|
|Transparency:||Transparent to Translucent, Opaque|
|Luster:||Adamantine to Vitreous, Pearly on partings|
|Refractive Index:||1.760 – 1.772 Uniaxial ( – ); commonly anomalously Biaxial|
|Birefringence:||0.008 – 0.009|
|Pleochroism:||Weak; e = blue-green to yellow-green, o = pale to deep blue|
|Other:||Asterism often present due to oriented needle-like inclusions or to colloidal or other material deposited in oriented tubules.|