Table of Contents Chapter: Earth Materials Section 1: Minerals Section 2: Igneous Rocks Section 3: Sedimentary Rocks Section 4: Metamorphic Rocks andthe Rock Cycle
Minerals 1 Common Elements Composition of Earth’s Crust • The crust is the outermost layer of Earth.
Minerals 1 What’s a Mineral? • A mineralis a naturally occurring element or compound that is inorganic, solid, and has a crystalline structure.
Minerals 1 Physical Properties • A mineral has a characteristics set of physical properties, but some of these properties can differ from sample to sample.
Minerals 1 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.
Minerals 1 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.
Minerals 1 Hardness • The physical property that measures resistance to scratching is called hardness.
Minerals 1 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.
Minerals 1 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.
Minerals 1 Crystal Shape • 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.
Minerals 1 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.
Minerals 1 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.
Minerals 1 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.
Minerals 1 Minerals From Evaporation • When water slowly evaporates, concentrated dissolved mineral may be left behind to form crystal.
Minerals 1 Mineral Groups Silicates • Silica is a common term for a compound that contains silicon plus oxygen or silicon dioxide (SiO2).
Minerals 1 Silicate Structures • The simplest silicate structures have silicon-oxygen tetra-hedrons that are not linked together. • By joining silicon-oxygen tetrahedrons together, chains, sheet, and three-dimensional framework structures can form.
Minerals 1 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.
Minerals 1 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.
Minerals 1 Important Non-silicates • To be an ore, a mineral must occur in large enough quantities to be economically recoverable.
Section Check 1 Question 1 Which is NOT a mineral? A. apatie B. flourite C. gold D. oxygen
Section Check 1 Answer The answer is D. A mineral must be a solid.
Section Check 1 Question 2 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.
Section Check 1 Question 3 How many crystal shapes have been identified? A. five B. six C. seven D. eight
Section Check 1 Answer The answer is B. Minerals can be classified by these six shapes.
Igneous Rocks 2 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.
Igneous Rocks 2 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.
Igneous Rocks 2 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.
Igneous Rocks 2 Nature of Magma • As crystals solidify in cooling magma, they use up certain atoms. • High-temperature magmas tend to crystallize first.
Igneous Rocks • Late-forming, less dense minerals tend to solidify at lower temperatures and float to the top of the magma chamber. 2 Nature of Magma
Igneous Rocks 2 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.
Igneous Rocks 2 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.
Igneous Rocks 2 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.
Igneous Rocks 2 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.
Igneous Rocks 2 Extrusive Igneous Rock Composition • A magma rich in silica (SiO2) 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.
Igneous Rocks 2 Extrusive Igneous Rock Composition
Igneous Rocks 2 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.
Igneous Rocks 2 Effect of Gases • A texture called vesicular forms near the top surface of a flow where gases escape.
Section Check 2 Question 1 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.
Section Check 2 Question 2 Igneous rocks form from molten rock material called _______. A. basalt B. silica C. magma D. granite
Section Check 2 Answer The answer is C. There are two types of igneous rocks; intrusive and extrusive.
Section Check 2 Question 3 Extrusive igneous rocks form when _______ cools. A. lava B. magma C. water D. volcanic glass
Section Check 2 Answer The answer is B. When magma reaches Earth’s surface it is called lava.
Sedimentary Rocks 3 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.
Sedimentary Rocks 3 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.
Sedimentary Rocks 3 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.
Sedimentary Rocks 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 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.
Sedimentary Rocks 3 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.