Which is a common characteristic of extrusive igneous rock?

a. cools slowly

b. forms crystals

c. contains small grains

d. contains large grains

The answer is; C

Extrusive rock is one that forms when magma finds its way to the surface of the earth. The lava cools quite fast compared to intrusive rock that cools before it reaches the earth's surface. Lava that cools fast forms small crystals. Examples of extrusive rocks include; basalt, obsidian, and rhyolite. Intrusive rocks cool slowly and form large crystals.

Extrusive igneous rock is formed by the crystallization of magma release after volcanic eruption at the Earth surface. They are characterized by fine grained textures because of rapid cooling they do not form large crystals. Extrusive rocks with fine grained textures are called aphanitic rocks. The most common extrusive igneous rock is basalt. Other examples include rhyolite, andesite and obsidian. Extrusive igneous rocks erupt quickly and they form small crystals. Some of these rocks cools slowly that they form glass. These rocks includes andesite, basalt, dacite, obsidian, pumice, rhyolite, scoria and tuff.

The common characteristic of extrusive igneous rock is the b. forms crystals

Rapid cooling of magma produces small crystal rocks.