|Gemstone||Crystal System||Density||Hardness||Refractive index||Treatments|
|Sapphire||hexagonal||4.00||9||1.762-1.770|| heat, fracture filling;
bulk diffusion with beryllium
Sapphire is an aluminum oxide, occurring in every color of the rainbow. When it is red, it is termed ruby. It is a stone of great hardness and durability. It can also have phenomenal characteristics like asterism (star sapphire) and color changing (like alexandrite). The color changing varieties are some of my favorites, having the ability to change color depending on whether they are viewed in daylight or incandescent light. The history of the sapphire dates back to at least the 7th Century BC, when they were used by the Etruscans. The sapphires used by the Etruscans, Greeks and Romans were imported from India and what is now Sri Lanka. Sapphires were reputed to protect kings from harm and envy. In the 13th Century, it was written that sapphires had the power to protect against poverty, make a stupid man wise and an irritable man good-tempered.