Sapphire

Sapphire is the name of a category of precious gemstones formed from the mineral class named corundum.[1]#3Corundum is high on the hardness chart [2], which typically translates to more valuable gemstones.

Sapphire is best known as a deep blue transparent stone having a distinct crystalline appearance. The blue color comes from the presence of impurities of titanium and iron. Both need to be present to create the dramatic blue presentation. [5] The most popular cuts for a sapphire are oval, round and cushion. [4]

Notes from Wikipedia
* In geology, the term mineral is usually reserved for mineral species: mineral species are crystalline compounds meaning they have well-defined chemical composition and a specific crystal structure.
* The International Mineralogical Association (IMA) is the premier global standards body for the definition and nomenclature of mineral species.

• References
• 1. Wikipedia
• 2. GemSociety.org
• 3. Here we are referring to corundum in the rock-forming sense.
• 4. FourMine.com
• 5. WebExhibits.com, Cause of Color (in gemstones)

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Chemical Formula	Al2O3
Color	White, Colorless, Blue, Green, Yellow, Orange, Brown, Pink, Purple, Gray, Black, Multicolored
Hardness	9
Crystal System	Trigonal
Refractive Index	1.76Â -Â 1.77
SG	3.9Â -Â 4.1
Transparency	Transparent to opaque
Double Refraction	.0008
Luster	Vitreous to adamantine
Cleavage	None, but may exhibit parting
Mineral Class	Corundum