Obsidian is an igneous rock classified as a natural volcanic glass. It forms from the rapid cooling of felsic lava, which is rich in silica (about 65 to 80 percent), extruded from a volcano. This rapid cooling prevents the formation of a crystalline structure, resulting in an amorphous glassy texture

. Key characteristics of obsidian include:

• It is typically black but can also appear in brown, green, red, or rare colors like blue or yellow due to trace elements and inclusions

• It has a smooth, glassy texture with a conchoidal fracture and a hardness of about 5 to 6 on the Mohs scale

• Chemically, it is similar to rhyolite and granite, consisting mainly of silicon dioxide (SiO₂) with minor amounts of other oxides

• It is considered a mineraloid rather than a true mineral because it lacks a crystalline structure

In summary, obsidian is an extrusive igneous rock formed by the rapid cooling of high-silica lava, resulting in a natural volcanic glass with a distinctive smooth and glassy appearance.