Is Obsidian Coarse or Fine

GrainColorRock Namefineblack (dark) coloredBasaltash particlesfine-grained ashTuffglasslight colored, frothyPumiceglassdark colored, glassObsidian

Why does obsidian have a fine grained texture?

Extrusive or volcanic rocks crystallize from lava at the earth’s surface. The texture of an igneous rock (fine-grained vs coarse-grained) is dependent on the rate of cooling of the melt: slow cooling allows large crystals to form, fast cooling yields small crystals. … Volcanic glass is called obsidian.

Is obsidian rough or smooth?

Obsidian is an extrusive rock that erupted out of a volcano. Most volcanic rocks are rough and jagged because they contain gas bubbles. But obsidian is smooth because it contains mostly of glass.