Answer:
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.