Date: 22nd December - 20th January

Obsidian is a naturally occurring volcanic glass formed as an extrusive igneous rock.

It is produced when felsic lava extruded from a volcano cools rapidly without crystal growth.

Pure obsidian is usually dark in appearance though the colour varies depending on the presence of impurities.

Iron and magnesium typically give the obsidian a dark green to brown to black colour. A very few samples are nearly colourless.

In some stones, the inclusion of small white radially clustered crystals of cristobalite in the black glass produces a blotchy or snowflake pattern.