magma Molten rock below Earth’s surface.
mineral Naturally-occurring solid that has a definite crystal structure.
molten Something that is melted.
organic Having to do with living things.
precipitates Solid substance that separates out of a liquid; a solid substance that was
once dissolved in a liquid and gets left behind when the liquid evaporates.
sediments Small particles of soil or rock deposited by wind or water.
Points to Consider
- What processes on Earth are involved in forming rocks?
- Stone tools were important to early humans. Do you think rocks are still important to
modern humans today?
4.2 Igneous Rocks
Lesson Objectives
- Describe how igneous rocks are formed.
- Describe the properties of some common types of igneous rocks.
- Relate some common uses of igneous rocks.
Introduction
This lesson will discuss igneous rocks, how they form, how they are classified, and some of
their common uses. Igneous rocks may or may not be found naturally where you live, but
chances are that you have seen materials made from igneous rocks. One of the most common
igneous rocks is granite (Figure4.9). Granite is used extensively in building materials and
making statues. Perhaps you have used a pumice stone to smooth your skin or to do jobs
around the house. Pumice is another example of an igneous rock (Figure4.10). Pumice is
used to make stone-washed denim jeans! Pumice stones are put into giant washing machines
with newly-manufactured jeans and tumbled around to give jeans that distinctive “stone-
washed” look. You also probably use igneous rock when you brush your teeth every morning.
Ground up pumice stone is sometimes added to toothpaste to act as an abrasive material
that scrubs your teeth clean.