Q 01/05

Which of these is NOT one of the three main groups of rocks?

A) Igneous

B) Tectonic

C) Sedimentary

D) Metamorphic

Answer · why

B) Tectonic

Tectonic describes plate movement, not a rock type; the three groups cycle into one another over geological time in the rock cycle.

Q 02/05

Igneous rocks form when what cools and hardens?

A) Mud and sand

B) Compressed shells

C) Magma or lava

D) Ice

Answer · why

C) Magma or lava

Slow cooling underground gives granite; fast cooling at the surface gives glassy or fine-grained rocks.

Q 03/05

Roughly what share of the Earth's crust, by volume, is igneous rock?

A) 65%

B) 75%

C) 85%

D) 95%

Answer · why

A) 65%

Sedimentary rocks make up only about 8 percent of the crust by volume, though they cover most of the land surface.

Q 04/05

The oceanic crust is about 99 percent made of which dark igneous rock?

A) Granite

B) Basalt

C) Obsidian

D) Marble

Answer · why

B) Basalt

The continents, by contrast, are dominated by granite and similar rocks called granitoids.

Q 05/05

Which rock, formed from compacted mud, makes up about 82 percent of the crust's layered rocks?

A) Sandstone

B) Limestone

C) Shale

D) Chalk

Answer · why

C) Shale

Two other layered rocks account for most of the rest.