Table of Contents Chapter: Earth Materials Section 1: Minerals Section 2: Igneous Rocks Section 3: Sedimentary Rocks Section 4: Metamorphic Rocks and the Rock Cycle
1 Minerals Common Elements Composition of Earth s Crust The crust is the outermost layer of Earth.
1 Minerals What s a Mineral? A mineral is a naturally occurring element or compound that is inorganic, solid, and has a crystalline structure.
1 Minerals Physical Properties A mineral has a characteristics set of physical properties, but some of these properties can differ from sample to sample.
1 Minerals Atom Arrangement Some physical properties are controlled by the orderly arrangement of atoms in a mineral s structure. The arrangement of atoms and the bonds between them can reflect the way a mineral breaks, how hard it is, and what types of crystal shape it has.
1 Minerals Atom Arrangement Minerals break along planes that cut across relatively weak chemical bonds, a smooth, flat surface is created. This is called cleavage. Some minerals do not split along well-defined flat surfaces. In such cases, a mineral will break unevenly. This type of irregular break is called fracture.
1 Hardness Minerals The physical property that measures resistance to scratching is called hardness.
1 Minerals Luster and Streak The way a mineral reflects light is the physical property known as luster. Metallic and nonmetallic. Metallic luster minerals reflect light in a way that a metal surface might.
1 Minerals Luster and Streak Nonmetallic luster, includes minerals that shine like glass or appear earthy or waxy. The color of mineral in powdered form is called streak.
1 Crystal Shape Minerals The orderly internal arrangement of atoms in a mineral often is indicated by its external crystal shape. The types of symmetry shown by the crystal are key elements in determining the crystal system to which a mineral belongs.
1 Minerals Mineral Formation Growth also is controlled by how fast atoms can migrate to the crystal and by the temperature and pressure conditions of the surroundings.
1 Minerals Minerals From Hot Water Some minerals are produced from hot water solutions rich in dissolved mineral matter. When hot water passes through cracks in cooler rock, minerals may form within the cracks.
1 Minerals Minerals from Magma Molten rock material found inside Earth is called magma. As magma cools, atoms slow down and begin to arrange into an orderly structure. Below the solidification temperature of a mineral, crystals of that particular mineral may form and grow.
1 Minerals Minerals From Evaporation When water slowly evaporates, concentrated dissolved mineral may be left behind to form crystal.
1 Minerals Mineral Groups Silicates Silica is a common term for a compound that contains silicon plus oxygen or silicon dioxide (SiO2).
1 Minerals Silicate Structures The simplest silicate structures have siliconoxygen tetra-hedrons that are not linked together. By joining silicon-oxygen tetrahedrons together, chains, sheet, and threedimensional framework structures can form.
1 Minerals Silicate Structures Quartz and feldspar group silicates make up most of Earth s continental crust. Earth s oceanic crust is denser and contains a larger percentage of silicates whose tetrahedrons are not linked together as much.
1 Minerals Important Non-silicates Many important mineral groups are not silicates. These include the carbonates, oxides, halides, sulfides, sulfates, and native metals. The non-silicate groups are a source of many valuable ore minerals and building materials.
1 Minerals Important Non-silicates To be an ore, a mineral must occur in large enough quantities to be economically recoverable.
1 Question 1 Section Check Which is NOT a mineral? A. apatie B. flourite C. gold D. oxygen
1 Answer Section Check The answer is D. A mineral must be a solid.
1 Question 2 Section Check Which is NOT a physical property of minerals? A. cleavage B. fracture C. hardness D. Mohs
Section Check 1 Answer The answer is D. Mohs is a scale used to determine the hardness of a mineral.
1 Question 3 Section Check How many crystal shapes have been identified? A. five B. six C. seven D. eight
1 Answer Section Check The answer is B. Minerals can be classified by these six shapes.
2 Igneous Rocks What s a rock? A rock is a naturally formed consolidated mixture containing minerals, rock fragments, or volcanic glass. Rocks are identified by their composition and texture. Texture is a description that includes the size and arrangement of the rock s components.
2 Igneous Rocks Intrusive Igneous Rocks Igneous rocks are those that form from molten rock material called magma. Such rocks also are called intrusive igneous rocks because they form within, or push into, regions of Earth s crust.
2 Igneous Rocks Nature of Magma As it passes through rock, magma might cause partial melting of the rock it intrudes. Geologists have learned that minerals melt at different temperatures, so some will melt when exposed to the thermal energy of the magma.
2 Igneous Rocks Nature of Magma As crystals solidify in cooling magma, they use up certain atoms. Hightemperature magmas tend to crystallize first.
2 Igneous Rocks Nature of Magma Late-forming, less dense minerals tend to solidify at lower temperatures and float to the top of the magma chamber.
2 Igneous Rocks Nature of Magma The composition of intrusive igneous rocks gives you clues as to where in Earth they formed. Igneous rocks with abundant quartz generally are associated with continental crust. Those with little or no quartz generally are associated with deep locations in continental crust or with oceanic crust.
2 Igneous Rocks Intrusive Igneous Rock Texture In intrusive igneous rocks, grain size, which means the size of individual mineral crystals, gives you clues as to how fast magma cooled. Magma that cools slowly, allows atoms time to migrate about and form large crystals.
2 Igneous Rocks Classification of Intrusive Igneous Rocks Rocks that are quartz-rich and contain potassium feldspar and plagioclase feldspar are called granite. Rocks with no quartz and abundant plagioclase feldspar and pyroxene are called gabbro. Peridotite is denser than gabbro, is composed mainly of olivine and pyroxene.
2 Igneous Rocks Extrusive Igneous Rocks Extrusive igneous rocks are those that cool from lava that has erupted at Earth s surface. These rocks may have the same compositions as intrusive igneous rocks, but they always will have different textures. Composition of the surrounding rock material will also affect the extrusive magma.
2 Igneous Rocks Extrusive Igneous Rock Composition A magma rich in silica (SiO 2 ) forms rhyolite if it cools rapidly. Similarly, gabbro s fine-grained volcanic counterpart is basalt, which is a common rock in Earth s oceanic crust.
2 Igneous Rocks Extrusive Igneous Rock Composition
2 Igneous Rocks Extrusive Igneous Rock Textures If cooling starts off slowly below the surface with large crystals, but then finishes at a faster rate to form small or no crystals, the extrusive rock is called porphyry.
2 Igneous Rocks Effect of Gases A texture called vesicular forms near the top surface of a flow where gases escape.
2 Question 1 Section Check What might you expect to find if you examined a rock under a microscope? Answer A rock is a naturally formed consolidated mixture containing minerals, rock fragments, or volcanic glass.
2 Question 2 Section Check Igneous rocks form from molten rock material called. A. basalt B. silica C. magma D. granite
2 Answer Section Check The answer is C. There are two types of igneous rocks; intrusive and extrusive.
2 Question 3 Section Check Extrusive igneous rocks form when cools. A. lava B. magma C. water D. volcanic glass
2 Answer Section Check The answer is B. When magma reaches Earth s surface it is called lava.
3 Sedimentary Rocks Rocks From Surface Materials Rock is a consolidated mixture of minerals. Some of these minerals could be in bits and pieces of other rocks. Such small bits and pieces are called clasts. Rocks inside Earth are protected from surface conditions. Rock exposed at the surface is attacked by the weather.
3 Sedimentary Rocks Transportation and Deposition Mechanical weathering processes break into smaller clasts. When clasts are transported to new locations, they often become rounded before being deposited. When clasts are loose on Earth s surface, they don t fit together perfectly. The empty space in between the grains is called porosity.
3 Sedimentary Rocks Transportation and Deposition When buried by more sediment deposited above them, clasts can be smashed together with such great force that they become compressed and stick together. This process is called compaction.
3 Transportation and Deposition Water moving between clasts carries dissolved minerals that can act as cement. This process is called cementation. Most of the time both compaction and cementation work together to make sedimentary rock. Sedimentary Rocks
3 Sedimentary Rocks Detrital Sedimentary Rock Detritus is another name given to clasts. Clasts can come in many sizes. In order of decreasing size, clasts are known as gravel, sand, silt, or clay.
3 Sedimentary Rocks Detrital Sedimentary Rock Geologists have found that size works well as a clue to the kind of environment in which a rock formed. It takes more force, or energy, to lift or move gravel than it does to lift or move sand.
3 Sedimentary Rocks Detrital Sedimentary Rock Detrital sedimentary rock composition depends on sources to rock material that were eroded, transported, and eventually deposited.
3 Sedimentary Rocks Detrital Sedimentary Rock Some minerals tend to be more common in detrital sediments because they are harder or more resistant to being dissolved. Geologists examine sedimentary rock compositions and try to reconstruct what happened to form them. The general rock name is determined by the clast size.
3 Sedimentary Rocks Detrital Sedimentary Rock Clast size also provides clues to help determine the deposition environment of the sediment that formed the detrital rock.
3 Sedimentary Rocks Chemical Sedimentary Rocks Precipitation If water receives more dissolved materials than it can hold in solution, then the excess must precipitate out as microscopic crystals. Evaporation The other option is for some water to evaporate. This leaves an oversupply of dissolved matter and again crystals.
3 Sedimentary Rocks Biochemical Sedimentary Rocks If sedimentary rocks contain the remains of living organisms they are called biochemical sedimentary rocks. Limestone is composed, of the remains of marine organisms that had hard parts made of calcium carbonate. Coal is sedimentary rock composed almost entirely of the carbon that remains after plant material is compressed underground.
3 Biochemical Sedimentary Rocks Coal goes through a series of changes as it forms from peat. Sedimentary Rocks Each stage of compaction drives out more impurities and leaves behind a more concentrated form of carbon.
3 Question 1 Section Check Small bits and pieces of rock are called. A. clasts B. fragments C. pebbles D. pieces
3 Answer Section Check The answer is A. The word clast is from the Greek klastos which means broken.
3 Question 2 Section Check Which is NOT a type of clast? A. clay B. gravel C. sediment D. silt
3 Answer Section Check The answer is C. The four types of clasts are gravel, sand, silt, and clay. Sediment can contain any of these types of clasts.
3 Question 3 Section Check is a type of biochemical sedimentary rock that humans use to make electricity. A. Coal B. Limestone C. Gypsum D. Quartz
3 Answer Section Check The answer is A. Coal is composed almost entirely of carbon.
4 Metamorphic Rocks and the Rock Cycle Metamorphic Rocks Metamorphic rocks, have been changed by some combination of thermal energy, pressure, and chemical activity. Any igneous, sedimentary, or metamorphic rock is subject to change through metamorphism.
4 Metamorphic Rocks and the Rock Cycle Metamorphic Rock Composition Changing Minerals Clay minerals tend to form micas with increasing metamorphic conditions. Some new minerals form by dehydration at higher temperature and pressure.
4 Metamorphic Rocks and the Rock Cycle Changing Minerals Deep burial or regional movements of large parts of Earth s crust and uppermost mantle cause regional metamorphism. Local contact of any preexisting rock with magma is called contact metamorphism.
4 Metamorphic Rocks and the Rock Cycle Changing Minerals Foliated textures in metamorphic rocks have lots of layers or bands. Nonfoliated metamorphic textures include rocks whose grains are in more random orientations.
Metamorphic Rocks and the Rock Cycle 4 Foliated Rocks The most common sedimentary rocks in Earth s crust are mudrocks. These rocks contain abundant clay minerals.
4 Metamorphic Rocks and the Rock Cycle Foliated Rocks Nonfoliated metamorphic rocks tend to have random crystal orientation and uniform grain size. Mineral grains tend to grow as the grade of metamorphism increases.
4 Metamorphic Rocks and the Rock Cycle Metamorphic Rock Classification Much like other rock types, metamorphic rocks can be classified based on texture and composition.
4 Metamorphic Rocks and the Rock Cycle Metamorphic Rock Classification Mineral composition provides clues about the original rock type before metamorphism, and indicates to what degree a rock had been metamorphosed.
4 Metamorphic Rocks and the Rock Cycle The Rock Cycle Processes of the rock cycle include any chemical and physical conditions that continuously form and change rocks.
4 Question 1 Section Check Which is NOT an agent of metamorphism? A. chemical activity B. pressure C. thermal energy D. wind
4 Answer Section Check The answer is D. Wind is responsible for erosion on some rocks but it does not help form them.
4 Question 2 Section Check Describe foliated metamorphic rocks.
4 Answer Section Check Foliated textures in metamorphic rocks have lots of layers or bands in them.
4 Question 3 Section Check Is there a beginning and end to the rock cycle? Answer No, the rock cycle is a continual process in which rocks change from one form to another.
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