Chapter 8: Rocks and Minerals

Section 2: Rocks

Section 3: Rock Cycle

1. A rock is composed of two or more minerals. There are many different kinds of rock and they can take thousands or even millions of years to form. They can be classified by the way they form. The three main types of rock are igneous, sedimentary, and metamorphic.

2. Igneous rocks – form from melted rock that cools.

a. Deep inside the Earth temperature and pressure increase enough to melt rock.

b. Magma is melted rock that does not reach Earth’s surface.

c. Lava is melted rock that appears at or above Earth’s surface.i. Volcanoes can erupt,

bringing a lava flow to Earth’s surface.

ii. Fissures are large cracks that can allow lava to ooze out in a lava flow.

3. There are two main types of igneous rock, extrusive and intrusive.

a. Extrusive igneous rocks form from lava

b. Intrusive igneous rocks form from magma

c. Crystal size is the main difference between intrusive and extrusive igneous rock.

i. Intrusive igneous rocks have large crystals.

ii. Extrusive igneous rocks have small or no crystals.

d. Light-colored often intrusive igneous rocks containing a high percentage of silica are called granitic.

e. Dark-colored often extrusive igneous rocks containing iron, magnesium, or calcium are called basaltic.

Intrusive Rocks Extrusive Rocks

Large crystals

Small crystals

Form from magma

Form from lava

Ex: basalt, obsidian

Ex: granite

Form from melted rock

BOTH

4. Sedimentary rocks form in layers from broken rock, shells, plants, and other materials.

a. Sediment is carried by rivers, ocean waves, mudslides, glaciers, the wind, and gravity.

b. It takes thousands to millions of years for sedimentary rocks to form.

c. There are 3 types of sedimentary rock: detrital, chemical, and organic.

5. Detrital rocks are made of grains from minerals or other rocks that have been compressed. a. Detrital rocks can be identified by the size of the

grains that make them up.

b. Examples include shale, siltstone, sandstone, and conglomerates.

6. Chemical rocks form when mineral-rich water evaporates from other chemical processes.a. Chemical rocks form

when seawater, geysers, salt lakes, or hot springs evaporate.

b. Example: rock salt

7. Organic rocks form from dead plants and animals that have been compressed.

a. If the rock is produced from layers of plants it is called coal.

b. If the rock is produced from organic sediment in the ocean, it is usually classified as limestone.

c. Chalk is a kind of limestone made from the fossils of tiny animals and algae.

Time, pressure, and heat, and events such as erosion and moving land masses, make new rocks out of old rocks.

8. Metamorphic rocks – form when existing rocks are heated or squeezed. They may recrystallize and change chemically. a. Foliated metamorphic rocks have visible

layers or long mineral grains.

b. Nonfoliated metamorphic rocks do not have layers or bands.

9. Rock Cycle – rocks change from one type to another over millions of years.

a. The model or diagram of the rock cycle shows rocks on a continuing journey.

b. A rock in any part of the cycle could become any other kind of rock.

The Rock Cycle

(Sing to the tune of "Row, Row, Row Your Boat“)SEDIMENTARY rock

Has been formed in layers Often found near water sources

With fossils from decayers

Then there's IGNEOUS rock Here since Earth was born

Molten Lava, cooled and hardened That's how it is formed

These two types of rocks Can also be transformed

With pressure, heat and chemicals METAMORPHIC they'll become.