English: Knapper: Perri Smith

Obsidian is a glassy-textured, extrusive igneous rock. It forms by either very rapid cooling of lava or by cooling of high-viscosity lava. The latter origin is the most common. Obsidian is usually black but can be other colors. Flow-banding may be present. Small, light-colored crystals may be commonly included in the glass - such rocks are called "vitrophyre". Sometimes, obsidian is encountered with whitish areas resembling snowflakes - "snowflake obsidian", which forms as the glass slowly devitrifies over geologic time.

The arrowhead seen here is a modern replica made from Oregon obsidian. The obsidian is mostly gray-colored and has flow-banding.