Geology Chapters 5 and 6 Science of Geology

Geology Chapters 5 and 6

Science of Geology 0 Geology is the study of planet Earth, including its composition and structure. 0 Scientists who study the Earth are called geologists.

Geologists Divide the forces that change Earth’s surface into two groups Constructive forces Destructive forces

Crust 0 Much of the crust is made up of silicates (compounds of silicon and oxygen) 0 Two different types of crust 0 Continental- less dense rock such as granite 0 Oceanic- more dense rock such as basalt

Rocks 0 Solid combination of minerals or mineral material 0 Much of the Earth’s surface is covered with plants and soil, but underneath is a layer of solid rock.

Rocks 0 Classified into three groups 0 Igneous- rock that forms from magma 0 Sedimentary- forms as sediment is squeezed and cemented together 0 Metamorphic- changed by temperature, pressure, or reactions with hot water

Rock Cycle A series of processes in which rocks continuously change from one type to another Caused by forces within the earth and at the surface

Minerals 0 Minerals are naturally occurring, inorganic solid with a crystal structure and a characteristic chemical composition. 0 Minerals are the building blocks of rocks.

Bowen’s Reaction Series Illustrates the order in which minerals crystalize.

Minerals 0 Properties to identify minerals: 0 Crystal structure 0 Color 0 Streak 0 Luster 0 Density 0 Hardness 0 Fracture and cleavage

Crystal Structure 0 In minerals, the atoms are arranged in a particular geometric shape, or crystal structure. 0 Some crystals are so small that you must use a microscope while others are as big as a telephone pole.

Color and Streak 0 Some minerals can be identified by a characteristic color. 0 The color or a mineral’s powder or its streak is not always the same color as the mineral itself.

Luster and Density 0 Luster is the way in which a mineral reflects light. Some minerals have a metallic luster while others have a vitreous (glassy) luster.

Density 0 Density is the minerals mass divided by its volume. It depends on the chemical composition.

Hardness 0 The resistance of a mineral to scratching. 0 A hard mineral can scratch a softer mineral, but not the other way around. 0 Scale ranges from 1 -10. Talc (1) – Diamond (10)

Fracture and Cleavage 0 How a mineral breaks 0 Cleavage is a type of fracture in which the mineral tends to split along regular, well defined planes where bonds are the weakest.

Other properties 0 Some minerals dissolve in acid. 0 Others are magnetic. 0 Some have unusual electrical properties.

Igneous Rocks 0 Magma is a mixture of molten rock and gases that forms underground. 0 Magma that flows out of volcanoes is called lava. 0 Intrusive rock- forms underground. 0 Extrusive rock- forms at the Earth’s surface.

Igneous Rocks 0 To identify igneous rocks: 0 Look at chemical composition and texture 0 Textures: 0 0 0 Coarse-grained Fine-grained Porphyritic (large and small crystals) Glassy Vesicular (full of holes)

Granite

Obsidian

Sedimentary Rock 0 Sedimentary rocks form through two main processes: 0 Compaction- the pore space between sediment grains is reduced by weight and pressure of overlaying sands 0 Cementation: is the process in which sediments are glued together by minerals that are deposited in water

Sedimentary Rocks 0 Clastic Rock- rocks that form from the broken fragments of other rocks held together by cement. 0 Chemical Rock- form when minerals precipitate out of solution. 0 Organic Rock- form as the result of organic processes. Shells and skeletons sink to the ocean floor. Over time, the fragments compact and cement together.

Characteristics of Clastic Sediments 0 The physical characteristics of sediments are determined mainly by the way sediments were transported to the place where they were deposited. 0 Four main agents: 0 Water 0 Ice 0 Wind 0 Gravity

Characteristics of Clastic Sediments 0 Sorting occurs when currents of air or water tend to separate sediments according to size. 0 Angularity is caused by collisions of particles during transporting. Particles that travel farther tend to be smoother.

Chert

Limestone

Conglomerate

Metamorphic Rock 0 Most metamorphic rocks form heat, pressure, and hot fluids deep underground. 0 Metamorphism can cause chemical changes and the texture of rocks. 0 Metamorphic rocks often have a striped appearance.

Two Types of Metamorphism 0 Contact- due to contact with magma 0 Regional- due to plate tectonics, and occurs over a large area

Textures of Metamorphic Rocks 0 Foliated: mineral grains are arranged in planes or bands 0 Nonfoliated: mineral grains are not arranged in plains or bands

Gneiss

Quartzite