Obsidian JewelryWhere the name comes from: The Ancient Greek philosopher Pliny mentions "Obsidianus" a volcanic glass named after Obsius who found a similar stone in Ethiopia.
Where the stones come from: World wide in areas of a particular type of volcanic eruption - rhyolitic, where the lava has cooled extremely quickly.
Chemistry: A volcanic glass. 70-75% Silicon dioxide, SiO2 - the remainder is magnesium and iron oxides, MgO and Fe3O4
Colors: Black, dark brown, dark green, also with a range of sheens from yellow, blue and rainbow caused by tiny included air bubbles. Snowflake obsidian has inclusions of white crystals in a black matrix.
...and another thing: As a form of glass, obsidian can form very sharp cutting edges, even today it can be used for scalpel blades which are much sharper and smoother than steel.