Study Guide: Chapter 2; Lesson 2 Classifying Rocks
Rock Forming Minerals: The minerals that make up rocks. Most rocks are made
of several kinds of minerals. Granite is made up of quartz, feldspar, mica and
hornblende.
Granite: A light colored intrusive igneous rock. It has coarse (big) grains. It
comes from magma deep under the Earth. It is made of the minerals quartz,
feldspar, mica and hornblende. Granite is the main rock in the continental
crust. Granite cools slowly under the Earth which makes it have coarse grains.
Basalt: A dark colored extrusive rock. It has fine (small grains. It comes from
volcanoes, usually under the ocean. These volcanoes are called seamounts.
Texture: The look and feel of the rock. This is caused by the grains in the rock.
Igneous Rocks: Rocks that come from lava or magma.
Intrusive Igneous Rocks: Intrusive igneous rocks form from magma deep under
the ground. They cool very slowly which makes them have coarse grains.
Extrusive Igneous Rocks: Extrusive igneous rocks form on top of the crust. They
are formed from. Lava cools quickly so the grains are very small. Some extrusive
rocks, such as obsidian have no grains.
Sedimentary Rocks: These rocks form over very long periods of time when small
grains of other rocks are deposited, compacted and cemented together.
Metamorphic Rocks: These rocks form deep under the crust when heat,
pressure and chemical reactions cause the rocks to change in some way.
Chapter 2; Lesson 3: Igneous Rocks
Intrusive Igneous Rocks: Rocks that form from magma deep under the ground.
Intrusive rocks cool very slowly so have coarse grains and large crystals. Granite
is the most common intrusive igneous rock. Granite is coarse grained and light
colored.
Extrusive Igneous Rocks: Rocks that form from the lava from volcanoes.
Extrusive rocks cool very quickly so they have fine small grain sizes. Basalt is a
fine grained dark extrusive igneous rock that comes from volcanoes, especially
seamounts, which are volcanoes under the ocean.
Volcanic Glass: These rocks lack a crystal structure and have no grains. They
come from volcanoes on land. Obsidian is an example of volcanic glass.
Uses: People throughout the world have used igneous rocks for tools and
building materials because they tend to be dense, hard and very durable.
Pumice is an extrusive igneous rock that comes from volcanoes. It has lots of air
pockets which cause it to have a coarse rough feel. Pumice is used an
abrasive for cleaning and polishing.
Chapter 2; Lesson 3: Sedimentary Rocks
Sedimentary rocks form from sediment which are small particles that come
from other rocks or living things. They form when sediment is deposited by wind
or water.
4 steps to form sedimentary rocks:
1] weathering / erosion
2] deposition
3] compaction
4] cementation
Weathering: The effects of freezing, thawing, plant roots and other forces on
rocks. These forces break rocks into small particles called sediment.
Erosion: Wind or water carries the small particles, or sediment, away after it is
weathered. Erosion can also occur by ice carrying particles away. This happens
when glaciers move.
Deposition: Material that is laid down in a certain area in many layers over a
long period of time. The materials settle out of the wind or water that is carrying
it.
Compaction: Layers of deposited sediment are squeezed tightly together.
Newer layers put a lot of weight on older layers causing it to compact even
more.
Cementation: Dissolved minerals crystallize and glue particles of sediment
together.
Clastic Rock: A sedimentary rock formed when rock fragments are squeezed
together. Examples of clastic rock are shale, sandstone, conglomerate, and
breccia.
1] Shale: forms from tiny particles of clay. This is a very fine grained rock.
2] Sandstone