Snowflake Obsidian and Obsidian

Obsidian (volcanic glass) is dark-coloured natural glass formed by the rapid cooling of silica-rich lava. As the lava is erupted from a volcano, it cools so rapidly that only glass and some microscopic crystals can form. These microcrystals create a black or dark green colour.

Obsidian is not chemically stable in the long term. Over time, parts of the randomly arranged glassy rock rearrange into regular patterns, creating a quartz-type mineral called cristobalite. This change in structure is known as devitrification. When polished these white inclusions in the obsidian look like snowflakes in the black rock, so this is called ‘snowflake obsidian’