Igneous Rocks

Which terms best describe igneous rocks?

• light and easily broken

• soft and smooth

• hard and dense

• soft and dense

Magma that is low in silica usually forms light-colored rocks, such as granite.

• True

• False

How do coarse-grained intrusive igneous rocks form?

• from sedimentary rocks changed under pressure

• from large rock particles cemented together

• from rapidly cooling lava

• from slow cooling magma

Basalt is used for cobblestones and in landscaping.

• True

• False

Which igneous rock is mixed with soil and used for starting vegetable seeds?

• perlite

• obsidian

• basalt

• granite

Igneous rocks are classified by their origin, texture, and mineral composition.

• True

• False

Which igneous rock is an extrusive rock?

• porphyry

• rhyolite

• pegmatite

• granite

Extrusive rocks have larger grains than intrusive rocks.

• True

• False

When all the grains in a rock are large and easy to see, the rock is described as

• Fine-grained

• Coarse-Grained

• Glassy

An igneous rock commonly used as building material is

• Slate

• Sandstone

• Granite