MF U1 L2.2 Igneous Rocks

Do you think that the rock in the picture took more or less time to cool than rocks that form from magma far beneath Earth’s surface? (page 26)

Answer explanation

The igneous rock formed from lava probably took less time because air temperatures above the Earth's surface are cooler than temperature's below the surface.

What happens to the matter in rock when it melts beneath Earth’s surface?

• The matter making up the rock is destroyed.

• It becomes magma that may cool and become another igneous rock.

• Mineral crystals grow.

• It is instantly transformed into igneous rock.

Which statement correctly describes the characteristics of igneous rocks and how they form? Select all that apply.

• Igneous rocks can be colors other than black.

• All igneous rocks are found near active volcanoes.

• All igneous rocks form beneath Earth.

• All igneous rocks form when molten rock solidifies.

• All igneous rocks are built from the same mineral components.

Compare the pictures of the igneous rocks. Which of the three rocks shows evidence of the longest cooling process?

What evidence do you see to support your answer?

Answer explanation

The middle rock appears to have the largest visible crystals and coarsest grain.

The large crystals and coarse grain indicate that the middle rock formed more slowly than the other rocks.

The igneous rock columns making up Devils Tower, Wyoming, show the result of magma forcing its way up toward Earth's surface. Geologists hypothesize that the columns formed underground. Them columns later became exposed after the surrounding rock eroded away. The rock formation was exposed and shaped by erosion.

Devil's rock cooled slowly underground and was exposed as a result of

• weathering

• erosion

• weathering and erosion

• volcanic eruption

Quick-cooling igneous rock often as a spongy appearance because the lava contained bubbles of gas. This leaves pockets of air in the rock. Pumice is an example of this type of igneous rock and can be light enough to hold above your head with little or no effort.

This rock was formed on the Earth's surface and is ______ rock.

• intrusive

• extrusive

Compare and contrast the two rock formations shown on page 11. Give one way the rocks are similar and one way they are different.

Answer explanation

Similar: Both rocks are formed from when melted rock cooled.

Different:

The rock in Devils Tower cooled slowly underground and was exposed as a result of weathering and erosion,

The pumice formed quickly as the lava was exposed to air, which trapped the gas bubbles in the rock.

What happens to the matter in rock when it melts beneath Earth's surface? How does the melting process eventually lead to igneous rock? (page 26)

Answer explanation

As rock melts beneath the surface it becomes magma.

The magma cools and solidifies to form igneous rock.