Rocks: Types of Rocks

Rocks: Types of Rocks

by Kylie Hockersmith

​Igneous Rock Formation

​Recall that lava is magma that has reached Earth’s surface during a volcanic eruption. What do you think of when you hear the word lava? Perhaps you picture hot, gooey liquid that flows easily. When lava cools and crystallizes, it becomes igneous rock. Lava cools quickly when it comes in contact with the cooler air. Not all magma makes it to Earth’s surface. Large amounts of magma cool and crystallize beneath Earth’s surface. No cool air comes in contact with the magma. As a result, the process of cooling and crystallizing takes much longer. Igneous rock that formed beneath Earth’s surface looks much different from rock that formed from lava cooling on Earth’s surface. They can also be classified as mafic, felic of intermediate depending on what the mineral and silica content is in the magma

Multiple Choice

What happens to lava when it comes into contact with the air

• turns red

• melts

• heats

• cools

Multiple Choice

What process forms igneous rocks 

• heat and pressure

• cooling and crytallization

• compaction

• deposition

Multiple Choice

Magma is molten rock when it reaches earths surface

• True

• False

​Igneous Rock Notes

​So....Igneous rocks are formed from molten rock either ON earths surface, OR underground.

​Intrusive=inside the earth

​-They are formed underground when magma slowly cools. Because they cool slowly, characteristics of them are that the crystals have time to grown nice and big, and visible and have a course texture. Some examples of Intrusive igneous rocks are granite, gabbro, diorite, and pegmatite.

​Extrusive=on earths surface

​-They are formed on the surface of earth after lava cools. Lava cools quickly because it comes into contact with the cooler air so characteristics of it are that the crystals are small, tiny, and have a fine texture. Some examples of extrusive igneous rocks are basalt, pumice, obsidian, and scoria.

Multiple Choice

An igneous rock that forms on earths surface is considered to be

• Intrusive

• Extrusive

• magma

• metamorphic

Multiple Choice

When magma forms an igneous rock the crystals are usually 

• small

• large

• non existent

• unnatractive 

​This is the end of igneous rocks. Make sure you have all the answers written down in your notes. If you have any blanks, click the back button to find those answers! Make sure your notes are colored

​Sedimentary Rocks

​You have already learned about the processes that form igneous rocks. Sedimentary rocks also form in different environments through a series of complex processes. Water and air can change the physical or chemical properties of rock. Rocks can break apart, dissolve, or form new minerals. When water travels through rock, some elements in the rock dissolve. The water can carry these elements to new locations. Water, glacial ice, gravity, and wind can all transport mineral and rock fragments to new locations. Eventually, the sediments are deposited, or laid down, and they can then build up in layers.

Multiple Choice

Which of these do not transport sediments from one place to another?

• still water

• wind

• running water

• glacial ice

​Compaction and Cementation

​Over time, sediment deposits become thicker. Layers of old sediment are buried by layers of younger sediment. Eventually, the old and young layers of sediment may be buried by even younger sediment. The weight from the layers of sediment forces out fluids and decreases the space between grains during a process called compaction. Compaction can lead to a process called cementation. When minerals dissolved in water crystallize between sediment grains, the process is called cementation. Mineral cement holds the grains together. Quartz, calcite, and clay are some of the common minerals that cement sediment together.

Multiple Choice

The weight from the layers of sediment forces out fluids and decreases the space between grains during a process called

• deposition

• weathering

• erosion

• compaction

Multiple Choice

When minerals dissolved in water crystallize between sediment grains, the process is called

• compaction

• deposition

• cementation

• erosion

​Sedimentary Rocks Notes

​They are formed from the sediments or small pieces of weathered rocks. They are compacted and cemented together to form a new rock.

​

​Some characteristics of sedimentary rocks if you can often see visible layers in the rocks. You may also see individual sediments in the rock

​

​Some examples of sedimentary rocks are sandstone, conglomerate, limestone, and coal.

​

​Fossils are often found in sedimentary rocks because dead plants and animals form fossils in the mud and sand and become cemented into the sedimentary rock

Multiple Choice

Dead plants and animals can be a part of a sedimentary rock 

• true

• False

​Metamorphic Rock Background

​Imagine that you left home with a cheese sandwich in your backpack. You threw your backpack into your hot locker at school. Would the sandwich look the same by lunchtime? The cheese would likely be soft because of changes in temperature. Also, your heavy backpack could squish the sandwich. Like the sandwich, metamorphic rocks are affected by changes in temperature and pressure. Metamorphism is any process that affects the structure or composition of a rock in a solid state as a result of changes in temperature, pressure, or the addition of chemical fluids

Multiple Choice

Which process causes metamorphic rocks to form

• extreme temperature and pressure

• weathering and erosion

• compaction and cementation

• melting

​Background continued...

​Most metamorphic rocks form far below Earth’s surface. Deep within Earth’s crust and mantle, temperatures and pressures are high. Metamorphic rocks, like igneous rocks, form under high temperature and pressure conditions. Unlike igneous rocks, metamorphic rocks do not crystallize from magma. If you compare metamorphic rocks to sedimentary rocks, you will notice differences. Sedimentary rocks form on Earth’s surface, while metamorphic rocks form beneath Earth’s surface. Erosion and deposition contribute to the formation of sedimentary rocks. These processes are not part of the formation of metamorphic rocks.

Multiple Choice

Igneous rocks usually form deep within earths crust, while metamorphic rocks usually form near the surface 

• True

• False

​Metamorphic continued...

​When rocks undergo high temperatures and intense pressure, they have properties similar to plastic. The rocks can bend and fold without melting. A permanent change in shape by bending and folding is called plastic deformation. These changes can cause a change that can be both physical, chemical, or both. The process is considered either "contact" or "regional".

Multiple Choice

What is it called when rocks undergo extreme temperature and pressure and start to bend and fold, without melting

• metamorphosis

• meta-analysis

• plastic deformation

• bend and snap

​Foliated vs. Nonfoliated Metamorphic

​Foliated Rocks The metamorphic rock schist is an example of a foliated rock. Foliated rocks contain parallel layers of flat and elongated minerals. Often, the layers are different colors. The layers develop from an uneven distribution of pressure during metamorphism. Foliation is a common feature of metamorphic rock.

​

Nonfoliated Rocks Nonfoliated rocks are metamorphic rocks that have mineral grains with a random, interlocking texture. In nonfoliated rocks, the minerals do not line up. Instead, the crystals are shaped like blocks and are all about the same size. The minerals are generally the same color, which helps distinguish them from igneous rocks such as granite.

Multiple Choice

A metamorphic rock with random crystals with no organized layers are referred to as 

• Foliated

• Non-Foliated

​Metamorphic Rock Notes

​They are formed underground when rocks are exposed to heat and pressure.​

Some characteristics of a metamorphic rock is that they have visible minerals that are stretched and squished. They maybe in layers(foliated) or not(non-foliated)

​

They often form near plate boundaries because the heat and pressure found at these boundaries are perfect conditions for them to form

​

​Some examples of metamorphic rocks are slate, marble, schist, and gneiss

Multiple Choice

Where do metamorphic rocks often form?

• in oceans

• deep underground

• in caves

• next to rivers