Sapphire Green

Sapphire is designated as the birthstone for September.
Green sapphire is a very durable gemstone.
Hardness of 9 second only to diamond
Crysatal structure Trigonal
Specific gravity 4.00
Refractive index 1.76-1.77
Luster Vitrous
Composition Aluminum oxide
Green Sapphire (Corundum)
Green sapphire was known from midieval times to the 19th century as "oriental peridot". Many sapphires that appear green actually consist of very fine alternating bands of blue and yellow sapphire, which may be visible under a microscope.
The most valuable color is a medium dark tone slightly bluish green or green with a very slightly grayish (cool) or very slightly brownish (warm) saturation.
Green sapphires are found in Thailand, Sri Lanka, Australia, and Montana.
Green sapphires from Montana in bluish green have the trade name "River" and the trade name "Evergreen" for their green sapphires.