ESci 03 Handouts 1

• Rocks


  Aggregates of a mineral or minerals
• There are over 5000 minerals, however only a few are necessary to identify most of the rocks
• Rock cycle


  • Fundamental concept that depicts the ever-changing transition through geologic times of the three (3) main types of rock: igneous, sedimentary, and metamorphic
  • Geologists group rocks into these categories on the basis of how rocks form
• Rock cycle


  Transformation of one (1) rock type to another through different processes
• All rocks may seem permanent and unchanging over a human lifetime, but this apparent permanence is an illusion created by our short observational time frame

  
• Over geologic time, water and air attack rocks of all kinds at Earth's surface
• Formation of igneous rocks


  When magma (molten lava) cools above or below ground
• Formation of sedimentary rocks


  When igneous rocks break down (due to weathering), they combine with other materials and then become compacted
• Formation of metamorphic rocks


  When the igneous and sedimentary rocks are changed by extreme heat or pressure
• Key Characteristics that Can Help in Classifying Rocks

  • Crystals
  • Fossils
  • Gas bubbles
  • Glassy surface
  • Ribbon-like layers
  • Sand or pebbles

  
• Types of Rocks


  • Igneous Rock
  • Sedimentary
  • Metamorphic
• Igneous Rocks


  • Some form when magma solidifies within Earth's crust; other igneous rock is created when magma erupts onto the surface
  • When magma solidifies, it usually crystallizes to form minerals
• Magma rises and heats large portions of the crust in places where tectonic plates converge
• Regional metamorphism


  Geological metamorphism involving a wide area and takes place at deeper regions of the crust
• Texture of igneous rocks

  Refers to the size, shape, and arrangement of its mineral grains, or crystals

  
• Igneous Rock Textures Based on Grain Size

  • Glassy
  • Very fine grained
  • Fine grained
  • Medium grained
  • Coarse grained
  • Porphyry

  
• Extrusive (Volcanic) Rocks


  Igneous rock that forms when magma rises all the way through the crust to erupt onto the Earth's surface
• Lava


  Fluid magma that flows from a crack or a volcano onto Earth's surface
• Obsidian


  Volcanic glass formed when molten lava hardens so quickly that the atoms have no time to align themselves to form crystals
• Intrusive (Plutonic) Rocks


  Igneous rock that forms when magma solidifies within the crust, without erupting to the surface
• Granite


  The most abundant rock in continental crust, a medium- or coarse-grained plutonic rock
• Formation of sedimentary rocks


  Weathering of rock, erosion, transport, and deposition of sediment, followed by compaction and cementation (lithification)
• Sedimentary Structures


  • Features that developed during or shortly after deposition of the sediment, help us understand how the sediment was transported and deposited
• Nearly all sedimentary beds were horizontal because most sediment accumulates on nearly level surfaces
• Mud cracks are irregular polygonal cracks that form when mud shrinks as it dries, indicating that the mud accumulated in shallow water are periodically dried up
• Ripple marks are small, nearly parallel ridges and troughs formed in sand and mud by moving water or wind
• Cross-bedding consists of small beds lying at an angle to the main sedimentary layers, forming in many environments where wind or water transports and deposits sediment
• Ripple marks


  • Small, nearly parallel ridges and troughs formed in sand and mud by moving water or wind
  • Often preserved in sedimentary rocks
• Cross-bedding


  • Small beds lying at an angle to the main sedimentary layers
  • Forms in environments where wind or water transports and deposits sediment
• Fossils


  Any remains or traces of a plant or animal preserved in rocks-any evidence of past life
• Foliation


  • A rock texture that looks like leaves of a book
• Contact metamorphism


  1. Hot magma intrudes cooler rock

  2. Metamorphic minerals grow with random orientations

  3. No metamorphic layering develops
• Burial metamorphism


  1. Rocks buried in a sedimentary basin

  2. Temperature and pressure increase

  3. Metamorphic minerals grow with random orientations

  4. Rocks are unfoliated
• Regional dynamothermal metamorphism


  1. Rocks deformed and heated at the same time

  2. Most common and widespread type of metamorphism

  3. Affects broad regions of Earth's crust
• Metamorphic grade


  The amount of metamorphism a rock has experienced
• Hydrothermal metamorphism


  1. Hot water and dissolved ions react with a rock to change its chemical composition and minerals

  2. Dissolves and accumulates metals from average crustal rocks

  3. Deposits the metals where temperature, pressure, or chemical environment changes
• Most rocks and magma contain very low concentrations of metals such as gold, silver, copper, lead, and zinc
• Metamorphic rocks result from changes to existing rocks due to heat, pressure, or chemical reactions.
• Metamorphic rocks result from changes to existing rocks due to heat or pressure.
• Sedimentary rocks form when sediments accumulate, compact, and cement together over time.