Obsidian is naturally occurring volcanic glass; it is formed during cooling at edges of lava field or where lava comes into contact with water. It ranks among general gemstones but not among genuine minerals because of its structure. It appears in shades of black, gray, brown, green, even bluish; it often has changing lanes of more colors. Dark colors appear due to presence of iron and magnesium, and possible other impurities can cause another color variants (rainbow glitter on rainbow obsidian, or combination with so-called cristobalite forming snowflake obsidian). It is transparent but opaque. These days it is found especially on the American continent in countries with past volcanic activity, but also in other countries with volcanoes (Iceland, New Zealand, etc.); in the Czech Republic it does not occur at all. Obsidian older than a million years is extremely rare, since this fragile material gets damaged in time. Obsidian was named after certain Roman called Obsius, as recorded by Pliny the Elder in his Naturalis Historia, who found similar stone in Ethiopia.
Obsidian was already used in the Paleolithic and Neolithic for making tools and weapons (blades, arrows for spears, etc.). The oldest evidence of use of obsidian is however already from around 700,000 years BC from region of what is now Kenya. It seems that specialized workshops producing objects of obsidian existed already in prehistoric times; and these objects were then distributed thousands of miles away. From prehistoric times, it has been used also for decorative purposes as evidenced by archaeological findings from pre-Columbian America (there was very advanced use of obsidian for decorations, tools and weapons) and Ancient Egypt (here for example so called necklace of Renisenib made of gold and obsidian created in years around 1810 to 1700 BC which is now on display in New York Metropolitan Museum of Art). Obsidian was imported to Egypt from the eastern Mediterranean and the southern Red Sea region. In Turkey and Israel, evidence was found of use of obsidian from the 5th millennium BC. Eye pupils of some human statues on Easter Island (Rapa Nui) (created between 1250 and 1500 AD) are made of obsidian. A number of esoteric functions is attributed to obsidian; mirror from this material was used to make contact with the spirit world, etc..
Even today it is used not only for jewellery and decorations, but also because of its minimal cleavage, conchoidal fracture and perfect blade for manufacturing of surgical instruments – the cutting edge can be with thickness of only 3 nanometers much sharper than the best steel, while significantly smoother and straighter at the same time.