Rocks

• Rock cycle


  Concept used to explain how the three basic rock types are related and how Earth processes, over geologic time, change a rock from one type into another
• Processes responsible for the continued recycling of rocks

  • Plate tectonic activity
  • Weathering
  • Erosional processes
• Main kinds of rocks

  • Igneous rock
  • Metamorphic rock
  • Sedimentary rock
• Conversion between rock types

  1. Cooling

  2. Melting

  3. Heat

  4. Weathering/erosion

  5. Compacting

  6. Cementing

  7. Pressure
• Magma


  Extremely hot liquid and semi-liquid rock located under Earth's surface
• Cooling


  Removal of heat, usually resulting in a lower temperature and/or phase change
• Crystallization


  Natural process which occurs as materials solidify from a liquid, or as they precipitate out of a liquid or gas
• Melting


  Change of a solid into a liquid when heat is applied
• Compaction


  Squeezing together of layers of sediment due to the great weight of overlying layers of rock
• Cementation


  Changing of sediment into rock by filling spaces around the sediments with chemical precipitates of minerals, binding the sediments, and forming solid rock
• Lithification


  Process of porosity destruction through compaction and cementation
• Heat


  Energy that is transferred from one body to another as the result of a difference in temperature
• Pressure


  Physical force exerted on an object
• Metamorphism


  Process of mineral assemblage and texture variation that results from the physical-chemical changes of solid rocks, caused by factors such as crust movement, magma activity, or thermal fluid change in the earth
• Weathering


  Breaking down or dissolving of rocks and minerals on Earth's surface
• Erosion


  Process that transports bits of rock and minerals away
• Sediment


  Solid material that is moved and deposited in a new location, consisting of rocks and minerals, as well as the remains of plants and animals
• Engineering definitions of rock differ from those used in geology; engineers consider rock to be a hard, durable material
• From an excavation point of view, rock is any material that cannot be excavated without blasting
• Another definition of rock indicates that it is earth material that does not slake when soaked in water
• Main types of rocks

  • Igneous
  • Sedimentary
  • Metamorphic
• Igneous rocks


  Formed when magma (molten rock) cools and crystallizes, either at volcanoes on the surface of the Earth or while the melted rock is still inside the crust
• Classification of igneous rocks


  • Texture
  • Mode of occurrence
  • Mineral composition
• Types of igneous rocks

  • Intrusive igneous rock
  • Extrusive igneous rock
• Intrusive igneous rocks


  • Characteristics by high crushing and shearing strengths, and unless too minutely fractured, they are usually satisfactory for all types of engineering construction and operations
  • Often good sources of concrete aggregates and other types of construction materials
  • Weathered igneous rock or any other weathered rock is to be avoided in foundations for engineering structures such as dams, bridges and underground installations
• Extrusive igneous rocks


  • Exhibit considerable variation in physical properties and usually require extended examination before their engineering characteristics can be evaluated
• Intrusive igneous rocks


  • Diabase
  • Diorite
  • Gabbro
  • Granite
  • Pegmatite
  • Peridotite
• Sedimentary rocks


  Formed on or near the Earth's surface from the compression of ocean sediments or other processes
• Geological processes that lead to the creation of sedimentary rocks

  • Erosion
  • Weathering
  • Dissolution
  • Precipitation
  • Lithification
• Sediments are a product of mechanical and chemical weathering, and are pieces of loose debris that have not been lithified
• Major types of sedimentary rocks

  • Chemical sedimentary rock
  • Clastic/mechanical sedimentary rock
• Chemical sedimentary rocks


  • Limestone
  • Dolomite
  • Diatomite
  • Chert and Flint
  • Peat, Lignite and Coal
  • Rock Salt
  • Chalk
• Flint


  A hard, tough, chemical or biochemical sedimentary rock that breaks with a conchoidal fracture. It is a form of microcrystalline quartz that is typically called "chert" by geologists. It often forms as nodules in sedimentary rocks such as chalk and marine limestones.
• Peat, Lignite and Coal

  • Peat is a deposit of dead plant material, the precursor to coal
  • Lignite is the lowest grade coal with the least concentration of carbon
  • Coal is an organic sedimentary rock that forms from the accumulation and preservation of plant materials, usually in a swamp environment
• Rock Salt


  The most abundant saline occurring in nature is sodium chloride. It is probable that salt deposits originated from evaporation of sea water.
• Chalk


  A variety of limestone composed mainly of calcium carbonate derived from the shells of tiny marine animals known as foraminifera and from the calcareous remains of marine algae known as coccoliths. Chalk is usually white or light gray in color. It is extremely porous, permeable, soft and friable.
• Gypsum and Anhydrite


  Pure calcium sulfate is known as anhydrite whereas the hydrated compound is known as gypsum. They are believed to result from precipitation from ocean water, and usually associated with beds of other marine sediments.
• Clastic sedimentary rocks


  • Classified by the shape of their grains (very angular, angular, rounded, or well-rounded)
  • The shape of the grains gives rocks their texture (may feel like sandpaper, or smooth and greasy)
  • Grains are carried by wind, water, or ice and bump into each other, breaking off corners and becoming smaller and smoother
• Clasts


  Fragments of rocks and minerals
• Breccia


  A clastic sedimentary rock composed of large angular fragments (over two millimeters in diameter). It is mainly used to make decorative architectural elements and may be polished to make decorative features or gemstones.