Obsidian

Obsidian, also known as Apache tears, is a volcanic glass which is generally black, but is occasionally red, brown, gray, green (the rarest variety), dark with "snowflakes," or even very clear. It is said, probably to be the most challenging stone in crystal work. It is in fact a volcanic glass and has been used in past by many native cultures to make knives.

Obsidian has several varieties. It contain tiny bubbles of air that are aligned along the layers created in the process of molten rock flowing just before being cooled. These captured bubbles produces interesting effects like golden sheen or a rainbow sheen. These types of stones are named as Sheen Obsidian and Rainbow Obsidian respectively. There is also Snowflake Obsidian, which has small, white and radially clustered crystals of cristobalite in the black glass and it produces a blotchy or snowflake pattern in it.

The stone is often confused with smoky quartz due the similar properties and also because of similar chemistry. It is found in Italy, Mexico, Scotland, Arizona, Colorado, Texas, Utah and Idaho. The specific gravity is 2.6 and hardness 5 - 5.5 on Mohs scale.

Techinical Specification

Name	Moh's	Specific Gravity	Structure	Cleavage	Refractive Index	Double	Disp.	Pleochro	Fluorescence
Obsidian	5+	2.3-2.8	Amorphous	None	1.48-1.51	None	0.010	None	None