This preview shows page 1. Sign up to view the full content.
Unformatted text preview: Rocks Rocks Rock: Rock: Aggregates consisting of one or more minerals more Three types of rocks Three Igneous Igneous Sedimentary Metamorphic Igneous Rocks Igneous Rocks Rocks that are formed from magma or lava lava Sedimentary rocks Sedimentary Rocks Rocks that are formed from weathered deposits of preexisting rock that had been transported, deposited, or lithified transported, Formed from sediments Metamorphic rocks Metamorphic Rocks Rocks that are produced from preexisting rocks which undergo large amounts of heat and pressure heat Igneous rocks Igneous These These rocks are produced from a molten material called magma material Once magma cools, it crystallizes and Once solidifies to form igneous rocks solidifies Magma normally consist of silicon, Magma oxygen, aluminum, iron, potassium, and sometimes water vapor sometimes Igneous Igneous rocks can be classified as either intrusive (plutonic) or extrusive (volcanic) intrusive Intrusive: Igneous rocks that are formed at Igneous depth (below the earth’s surface) depth Extrusive: Igneous rocks in which molten Igneous rock solidifies at the earth’s surface rock Igneous Igneous rocks can be classified based on texture and mineral constituents texture mineral Igneous Textures Igneous Texture: Texture: Describes the overall appearance of an igneous rock appearance Texture is based on size and arrangement Texture of crystals within the rock of Texture reveals a great deal about the Texture environment in which the rock is formed environment Types of textures Types Fine-grained Coarse-grained Coarse-grained Porphyritic glassy Fine grained texture Fine Rocks Rocks possess crystals which are too small to be seen by the unaided eye small Consist of small voids, called vesicles Consist vesicles Examples: rhylolite, scoria Coarse-grained texture Coarse-grained These These rocks have the appearance of a mass of intergrown crystals, which are large enough to be seen with the unaided eye eye Examples: Granite Porphyritic Texture Porphyritic Consist Consist of large crystals embedded in a matrix of smaller crystals matrix Example: andesite porhyry Glassy texture Glassy Usually Usually results when molten rock cools very rapidly (especially during volcanic eruptions) eruptions) Rock will take a glassy appearance Examples: obsidian, pumice Igneous compositions Igneous Igneous Igneous rocks are composed mainly of silicate minerals silicate Silicon and oxygen are the abundant Silicon constituents of igneous rocks constituents Other elements include aluminum, Other calcium, iron, potassium, sodium, and magnesium magnesium As As magma cools and solidifies, elements combine to form two major types of minerals: 1) dark silicates and 2) light silicates silicates Dark silicates vs. light silicates Dark Dark Dark silicates: Rich in iron and/or Rich magnesium and have a low silica content magnesium low Examples: olivine, pyroxene, amphibole Examples: Light silicates: Rich in sodium, potassium Light Rich and calcium, and have a higher silica and and higher content than the dark silicates content Examples: quartz, feldspar, muscovite mica mica Dark silicates vs. light silicates (cont.) (cont.) Basaltic Basaltic rocks that contain a high percentage of dark silicate minerals are referred to as mafic Granitic rocks which contain a high Granitic percentage of light colored silicate minerals are referred to as felsic minerals Further classification of igneous rocks rocks Granitic Granitic rocks: consist almost entirely of light colored silicates quartz and feldspar light These rocks are rich in silica and are major constituents of the continental crust major They are also involved in mountain building. building. Examples: Granite, rhyolite Examples: Basaltic Basaltic rocks: These rocks contain large amounts of dark silicate minerals (iron and magnesium) magnesium) Examples: basalt, gabbro Examples: Weathering Weathering Weathering: Weathering: The disintergration and decomposition of rock at or near the surface of the earth surface Types of weathering Types Mechanical Mechanical weathering: This is when rock is broken into smaller and smaller pieces is Chemical weathering: This is when rock Chemical undergo alteration of its chemical structure by removing and/or adding elements by Mechanical weathering Mechanical Mechanical Mechanical weathering increases the amount of surface area available for chemical weathering by breaking rocks into smaller and smaller pieces into Three processes that break rocks into Three smaller fragments: 1) frost wedging 2) unloading and 3) biological activity unloading Frost wedging Frost Frost Frost wedging: This is when water works into the cracks of a rock. Water will freeze and expand the opening. The process of many freeze-thaw cycles The will break the rock into pieces will Very common in mountainous regions Unloading Unloading Unloading: Unloading: This is the breaking off of rock into entire slabs. Also known as “sheeting” “sheeting” During unloading, outer layers of rock will During expand more than the rock below, and will separate from the rock body separate Biological activity Biological Weathering Weathering is also aided by the activites of organisms (plants, animals and humans) humans) Examples: Examples: - Plants growing into the fractures of rocks - Burrowing animals (moles, gophers) break Burrowing down rock by moving fresh material to the surface surface Chemical weathering Chemical During During chemical weathering elements are added and/or removed from rocks added Water is the most important agent in Water chemical weathering chemical Oxygen (dissolved in water) causes Oxygen oxidation of materials oxidation Carbon dioxide (dissolved in water) Carbon produces carbonic acid. ...
View Full Document
- Fall '10