Chapter 4 Rocks
Dec 30, 2015
Chapter 4Rocks
Classifying Rocks
Section 1
Why must scientists who study rocks look at the inside of them? Because the outside surfaces have been
exposed to the effects of ice, water, and weather (Erosion).
Mineral composition and color
2. What three important things do scientists observe when studying rocks?
-Mineral composition, color, and texture3. What are rock forming minerals?
-About 20 minerals that are found in the earth’s crust that make up rocks.4. What minerals are found in granite?
-Quartz, horneblende, mica, and feldspar
Mineral Composition:(This is also in the igneous section on page 2)
Most of Earth’s (rocks) contain Silica Silica is a material formed from oxygen and
silicon. The silica content of magma and lava will
affect the types of rock that form High silica usually forms light colored rocks Low silica usually forms dark colored rocks
5.Some other ways scientists study rocks include:
Shape and color of the crystals Mineral content Color Texture And some other tests similar to the tests for
minerals
TextureGrains- Give the rock textureWhat is texture?Texture is the look and feel of the rocks surface.The three grain sizes that make texture are:1.Fine2.Coarse3.No visible
Texture: Grain Size Coarse grained = large grains and easy to see
Fine grain = microscopic and too small to see
There are three main groups of rocksIgneous – forms from cooling of magma or lava
Sedimentary – forms when particles of other rocks or the remains of plants and animals are pressed and cemented together
Metamorphic – forms when and existing rock is changed by heat, pressure or chemical reactions, forms deep underground
There are two grain shapes:1. Jagged 2. Round
There are two grain patterns:1. Banded 2. Non- banded
Igneous Rocks
Section 2
Igneous Rocks An igneous rock is any rock that forms from
magma or lava. The name “igneous” comes from the Latin
word meaning “fire” Igneous rocks come from deep within the
ground
Igneous Rock Identification Igneous rocks are classified according to
origin, texture and mineral composition Origin Texture Mineral composition
Intrusive and ExtrusiveExtrusive rock is formed from lava that erupted onto the earth’s surface.
Intrusive rock is formed when magma hardens beneath the surface.
Molten rock below the earth’s surface is called magma. When it makes it to the surface it is called lava.
Igneous IDQuestions 5-7Texture: depends on the size and shape of the mineral crystals. The only exceptions are those rocks made of glass.
Rapidly cooling lava forms fine-grained rock Slowly cooling lava forms coarse-grained rocks
with large crystals Intrusive rocks should have coarse-grained
texture while extrusive rock will have fine-grained texture.
Igneous Rocks Continued Most of the earth’s rocks contain the mineral
silica. Silica content of rocks can affect the rocks
color.Examples of Igneous rocks:Rhyolite, Porphyry, Pegmatite, Granite, etc.
Uses of Igneous Rock Building Material
granite Cleaning and polishing
Pumice Sharp tools for cutting or scraping
obsidian
Sedimentary Rocks
Section 3
Sedimentary RockSediment - small, solid pieces of material that come from rock or living things.
Ex. rock, shells, bones, leaves, stems, etc.Sedimentary rocks are formed through the process of:
1.Erosion2.Deposition3.Compaction4.Cementation
Rocks
From Sediment to Rock
Most sedimentary rocks are formed through a series of processes: erosion, deposition, compaction, and cementation.
- Sedimentary Rocks
Sedimentary Rocks*Erosion*Erosion- destructive forces including heat, cold, rain, waves, grinding ice, running water, wind and ice loosen and carry it away. (The forces of erosion form sediment)
Sedimentary Rocks*Deposition*Deposition - the process by which sediment settles out of the water or wind carrying it
Sedimentary Rocks*Compaction*
Compaction - the process that presses sediments together
Thick layers build up over millions of years The more layers, the more it presses down on the
layers beneath them.
Sedimentary Rocks*Cementation*
Cementation - the process in which dissolved minerals crystallize and glue particles of sediment together
While compaction is occurring, the minerals slowly dissolve in the water
Sedimentary Rocks 3 major types of rocks
Clastic Organic Chemical
Sedimentary Rock: ClasticClastic rock- a sedimentary rock that forms when rock fragments are squeezed together
Sediments can range in size Ex. shale, sandstone, conglomerate, breccia
Sedimentary Rocks: OrganicOrganic rock- forms where the remains of plants and animals are deposited in thick layers
Ex. coal, limestone
Sedimentary Rocks: ChemicalChemical- when minerals that are dissolved in a solution crystallize
Ex. rock salt
Rocks From Reefs
Section 4
http://www.youtube.com/watch?v=60jof35WuAo
http://www.brainpop.com/science/diversityoflife/coral/
Rocks from Reefs1.These rocks are made from the exoskeletons of coral animals.2. Life can only live within the first 40 meters because that is where there is enough light.3. The exoskeletons are made from calcium.4. A coral reef forms when the animals die and their skeletons remain building up over time.5. Temperatures must be warm.6.Limestone deposits can tell us that there must have been on ocean or sea there sometime in the past
Metamorphic Rocks
Section 5
http://www.brainpop.com/science/earthsystem/typesofrocks/
Metamorphic RocksHeat and pressure beneath the surface of the earth can change any rock into a metamorphic rock.Geologists classify metamorphic rocks according to the arrangement of the grains that make up the rocks
Foliated Rocks Non-foliated Rocks
Metamorphic Rocks When a rock becomes a metamorphic rock…
Its appearance changes Texture changes Crystal structure changes Mineral content changes
Metamorphic Rocks Foliated = grains arranged in parallel layers or
bands Ex. slate, schist and gneiss
Metamorphic Rock Non-foliated = mineral grains are arranged
randomly Ex. marble, quartzite
Uses of Metamorphic Rocks Two of the most used metamorphic rocks
Marble – building and sculptures Lincoln Memorial
Slate – flooring, roofing, walkways, chalkboards
The Rock Cycle
Section 6
The Rock Cycle
Forces deep within the Earth and at the surface, produce a slow cycle that builds, destroys, and changes the rocks in the crust.
The rock cycle is a series of processes that change rocks from one kind to another.
Quartz
Sediment
Compaction
Cementation
Sedimentary Rock (sandstone)
Buried Pressure
Heat
Metamorphic Rock (quartzite)
What next?
ROCK CYCLE ACTIVITY