Why is obsidian considered a granitic rock?

Answer 1

Obsidian is an extrusive igneous rock because it is formed from the rapid cooling of magma after eruption ontoEarth's surface. The rapid cooling of lava results in a fine-grained texture, or in this case (with obsidian), a glassy texture, where cooling takes place so rapidly that mineral crystals do not have time to form. Rock that is formed from slow cooling magma beneath the surface is intrusive igneous rock, and exhibits visible mineral crystals.
Obsidian is an extrusive igneous rock.

Answer 2

Obsidian is a name given to a type of igneous rock. Obsidian is extrusive, meaning it forms outside the earth in open air as opposed to inside the ground. Obsidian is considered a glass (meaning it has no crystalline structure).

Obsidian forms from high-silica lava which cools so quickly that crystals do not have time to form. In order for lava to cool that quickly, it pretty much needs to form outside in the cool open air (making it extrusive). Magma underground basically can't solidify fast enough to form a obsidian.

Answer 3

Because it is naturally occurring and formed by processes which create igneous rocks.

Answer 4

Volcanic glass is considered an extrusive rock because it can form above the earth's surface.

Answer 5

Obsidian, even though it is a volcanic glass and an extrusive igneous rock, shares the same chemistry as intrusive granite; in other words they are both felsic igneous rocks.