Question

slow cooling magma produces ____ crystals. fast cooling magma produces __ igneous rocks. sometimes, the cooling is so __ as to prevent the formation of even small crystals, resulting in rock that may be mostly ____ such as obsidian.

Explanation:

1. For the first blank: Slow cooling of magma allows more time for mineral crystals to grow, so it produces large crystals.
2. For the second blank: Fast cooling magma doesn't give crystals much time to grow, so it produces small crystals in igneous rocks.
3. For the third blank: When cooling is extremely quick (too rapid), crystal formation is prevented.
4. For the fourth blank: Obsidian is a glassy rock, so when cooling is too rapid, the rock is mostly glassy (the term here refers to having a glass - like texture, as obsidian is a volcanic glass).

Answer:

1. large
2. small
3. rapid
4. glassy