Obsidian is a naturally occurring volcanic glass formed as an extrusive igneous rock It is named after the roman Obsius. In the past used to make Amulets and necklaces to protect the wearer from harm. It was also used in the making of weapons as it is very hard. Pure obsidian is usually dark in appearance, though the color varies depending on the presence of impurities. Iron and magnesium typically give the obsidian a dark green to brown to black color andsome stones, the inclusion of small, white crystals in the black glass produce a blotchy or snowflake pattern which is know as snowflake obsidian. it has a mohls hardness of 5-5.5 and a refractive index of 1.45-1.55