Blue obsidian is a pale blue rock that resembles glass. It is formed when viscous lava (containing high levels of silica and low levels of water) cools at a rapid rate with minimal crystal formation. It has a chemical composition similar to rhyolite. Obsidian is harder than glass and tends to produce sharp edges when it fractures and has historically been used for windows and for cutting and piercing tools (such as scalpel blades).
Not all obsidian has a blue color, some is a black or deep green color, and thus blue obsidian, which sometimes has an electric blue hue, is highly prized. There are some natural deposits located in Greece and the Atlas mountains in Morocco but it is extremely rare and many blue obsidian stones are man-made as a result. Today people prize it for use in jewelry and because it is believed to help achieve transcendence.