Obsidian is a volcanic glass that forms when lava cools very quickly and consists of a solid mass of glass through and through. Why is obsidian not classified as a mineral? Choose one: Obsidian is not naturally occurring since it is only associated with volcanoes. Obsidian does not have a definable chemical composition because it only comes from lava. Obsidian contains carbon-to-hydrogen bonds. The atoms or molecules in obsidian do not have a crystalline structure.

Obsidian is not a mineral as the atoms or molecules in obsidian do not have a crystalline structure.

Explanation:

Obsidian originates naturally and is formed by igneous rock.

When felsic larva comes out from the volcano,it rapidly cools down and thus form obsidian.It is pure black in color but some times color differ due to presence of some impurities.

It is brittle,but hard.It is not a mineral and is called as mineraloids and is not found in crystalline form,.

The main constituent is SiO2.

It is found in the margin of rhyolitic lava.