Obsidian: An Extrusive Igneous Rock

By: Faith Watts

Physical Characteristics

It is black and has a glassy look to it. It is smooth and generally lacks open voids or large bubbles like other volcanic rocks. It also can show sheens of gold or green, yellow, blue and/or purple coloration. Sometimes with white inclusions (Snowflake Obsidian).

What it is Made of?

It is a naturally occurring volcanic glass. It is made up of the magma that hadn't made it to the surface and rapidly cooled, making it it's deep black color.

How and Where Is It formed?

It is produced when felsic lava extruded from a volcano cools rapidly with minimum crystal growth.

What is the Rock Used For?

It was used to make knives, arrowheads, spear points, scrapers, and many other weapons and tools. Also, it is now used for mining.