Chapter 6 Outline/Study Guide
Rocks and the Rock Cycle
Rock – earth material made of minerals, glass or organic matter.
The three different types of rocks on Earth are
1. Igneous
2. Sedimentary
3. Metamorphic
Rock cycle – a series of processes on Earth’s surface and interior that slowly changes rocks
from one kind to another.
*Remember any rock can change to another rock by going through one or more processes.
The Rock Cycle
Compaction and
Cementation
Sediments
Weathering and
erosion
Sedimentary Rocks
Weathering
and erosion
Weathering
and erosion
Igneous Rocks
Heat and
pressure
Heat and
pressure
Weathering
and erosion
Heat and
pressure
melting
Cooling and hardening/
crystallization
melting
Metamorphic Rocks
melting
Magma
*The bolded items are the products and the processes are located on the lines.
Igneous Rocks
(examples – gabbro, obsidian and granite)
Igneous rocks form when magma or lava cools and hardens.
There are intrusive and extrusive igneous rocks.
Intrusive – igneous rocks that form below Earth’s surface (plutonic)
- coarse-grained (grains are large enough to be seen with your eye)
- all intrusive rocks contain minerals
Extrusive – igneous rocks that form on Earth’s surface and cool as lava (volcanic)
- fine-grained (grains are too small to be seen with your eye)
Mafic
1. dark-colored
2. rich in iron and magnesium
3. low silica content
4. magma is thin and fluid
Felsic
1. light-colored
2. rich in silicon and oxygen
3. high silica content
4. magma is thick and slow-flowing
If an igneous rock has a porphyritic texture it has two distinctly different textures because
there were two stages of cooling – slow and then fast.
Vesicular texture- this happens when the magma has gases in it causing the rock to form holes
when it cools.
Sedimentary Rocks
(examples- breccia, coal, shale and rock salt (halite))
Sedimentary rocks form when sediments become pressed or cemented together (compaction
and cementation)
Sediments – loose materials such as rock fragments and mineral grains that have been
transported by wind, water or glacier.
Weathering – the breaking of rocks into smaller pieces, either mechanically or chemically.
Erosion – the process that moves weathered rocks from one location to another.
Deposition – the build up of sediments on the bottoms of lakes, valleys and the ocean floor
usually in layers.
Compaction – when layers of sediment become compressed by the weight of layers above
them.
Cementation – when sediments are glued together by minerals deposited between the
sediments.
The three types of sedimentary rocks are clastic, chemical and organic
1. clastic – made up of broken fragments of plants, animals and primarily other rocks.
- The formation of a clastic rocks begins when water breaks, moves and relocates
rock.
- conglomerate – made of rounded, pebble-sized fragments that are held together
by cement.
- breccia – made of angular pebble-sized fragments that are held together by
cement.
- Sandstone- made of small mineral grains (usually quartz) that are cemented
together.
- Shale – made of flaky clay particles that compress into flat layers.
2. chemical sedimentary rocks – made from minerals precipitated from a solution or are
left behind when a solution evaporates. (example – halite (rock salt))
3. organic – made from the remains of once living things. (examples – limestone, chalk,
coal, )
Fossils can be found in sedimentary rocks.
Metamorphic Rocks
(examples – gneiss, slate, schist, quartzite and marble)
Metamorphic rocks form from existing rocks when the temperature or pressure
changes.
The two textures of metamorphic rocks are foliated and nonfoliated.
Foliated – when mineral grains flatten and line up in parallel bands.
Nonfoliated – when mineral grains change, grow, and rearrange but do not form bands.
Local metamorphism – metamorphism that affects a small volume of rocks.
Regional metamorphism – metamorphism that affects thousands of cubic kilometers of
rock.