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Rocks Notes
8th Science
Lane
Section One
The Rock Cycle
I.
What is a rock
a. Forming rocks
b. The Rock cycle
Section Two
I.
Igneous Rocks
Origin of Igneous Rocks
Igneous rocks come from volcanoes or volcanic processes.
a. Magma
Magma is rock material melted by heat and pressure. Magma will rise in
the Earth.
When magma reaches the Earth’s surface, it will flow as lava.
b. Intrusive Rocks
Intrusive rocks form below the Earth’s surface.
Mineral grain size depends on how quickly the magma cools.
c. Extrusive Rocks
Extrusive rocks form when lava cools on the Earth’s surface.
The mineral grains in extrusive rock is usually very small.
II.
Classification of Igneous Rocks
Igneous rock is classified by where it forms and the type of magma it forms
from.
a. Basaltic Rocks
Basaltic rocks are heavy and dark colored. The magma flows easily.
b. Granitic and Andesitic rocks
Granitic rock is light-colored and lighter than basaltic rock. The magma
flows stiffly.
Section Three
I.
Metamorphic Rocks
Origin of Metamorphic Rocks
Metamorphic rocks have been changed by heat and pressure.
a. Metamorphic Rocks
Metamorphic rocks are formed from igneous, sedimentary, or
metamorphic rocks.
b. Heat and pressure
If the heat is not enough to melt the rock it is changed to a metamorphic
rock.
Examples:
Shale—slate—schist—gneiss
Granite—gneiss
Basalt—schist
II.
Classification of Metamorphic Rocks
Metamorphic rocks are classified by their source and texture.
a. Foliated Rocks
Foliated rocks have bands or layers.
b. Nonfoliated Rocks
Non-foliated rocks do not have bands.
Examples:
Limestone—marble
Dolstone—dolmitic marble
Section Four
I.
Sedimentary Rocks
Origin of Sedimentary Rocks
a. Sedimentary Rocks
Sedimentary rocks form when sediments become pressed or cemented
together.
Sediments are usually formed from pre-existing rock being broken into
small pieces.
b. Compaction
Compaction is the pressing down of upper layers on the lower layers.
c. Cementation
Cementation occurs when a chemical glues the sediments together.
d. Sedimentary Rock Layers
Many types of sedimentary rock form layers. Usually the oldest layers are
on the bottom.
II.
Classification of Sedimentary Rocks
Sedimentary rocks are classified by their composition and they way they are
formed.
a. Detrital Sedimentary Rocks
Detrital rocks are formed from broken fragments of other rocks.
i. Clastic Texture
Clastic refers to a material being made of broken fragments.
ii. Shape and Size of Sediments
Detrital rocks are named for the shape and size of the sediments.
Breccia is made of pebbles that are sharp.
Conglomerate is made of pebbles that are rounded.
Sandstone is made of grains of minerals.
Shale is made of clay-sized particles.
b. Chemical sedimentary Rocks
These are made when a chemical precipitates from a solution, or water
dries and leaves them behind.
i. Limestone
Calcium carbonate is carried by seawater. It is deposited on ocean
floors as limestone.
ii. Rock Salt
When an ocean evaporates, it leaves behind the salt. This salt is
mostly halite.
c. Organic Sedimentary Rocks
Organic sedimentary rocks come from living things.
One type of organic rock is fossil-rich limestone.
Coquina has large shells.
Chalk has microscopic shells.
Coal is the remains of plants and animals.
III.
Another Look at the Rock Cycle