module 3

• 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


  A fundamental concept that depicts the ever-changing transition through geologic times of the three (3) main types of rock: igneous, sedimentary, and metamorphic
• 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
• 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, others are created when magma erupts onto the surface
  • When magma solidifies, it usually crystallizes to form minerals
• Regional metamorphism


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

  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 quickly with no time for crystals to form
• 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, erosion, and deposition of sediment, followed by compaction and cementation (lithification)
• Sedimentary structures


  Features that developed during or shortly after deposition of the sediment, helping to understand how the sediment was transported and deposited
• Nearly all sedimentary beds were horizontal because most sediment accumulates on nearly level surfaces
• 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
• Apatite


  A phosphate mineral, the most abundant phosphorous-bearing mineral. Covers three different minerals (fluorapatite, chlorapatite, and hydroxylapatite) depending on the predominance of fluorine, chlorine, or the hydroxyl group.
• Apatite


  • Widely distributed in all rock types (igneous, sedimentary, and metamorphic), usually as small disseminated grains, or cryptocrystalline fragments. Large, well-formed crystals can be found in certain contact metamorphic rocks.
• Apatite


  • Chemical composition - Ca5(PO4)3(OH, F, Cl)
  • Hardness - 5
  • Specific gravity - 3.1-3.2
  • Transparency - Transparent to translucent
  • Color - Typically green but also yellow, blue, reddish brown and purple
  • Streak - White
  • Luster - Vitreous to greasy
  • Cleavage/fracture - Poor / conchoidal
  • Crystal habit/mode of occurrence - Prismatic (hexagonal prism with hexagonal pyramid orpinacoid or both as termination)
• Augite


  A member of the pyroxene group of simple silicates, in which the SiO4 tetrahedra are linked by sharing two (2) of their four corners to form continuous chains. Often referred to as single chain silicates.
• Augite


  • Commonly found in igneous rocks such as gabbros, basalts and andesites, and high grade metamorphic rocks (granulites).
• Augite


  • Chemical composition - (Ca, Na)(Mg, Fe, Al)(Al, Si)2 O6
  • Hardness - 5-6
  • Specific gravity - 3.2-3.6
  • Transparency - Transparent to mostly translucent or opaque
  • Color - Dark green, brown and black
  • Streak - Greenish white
  • Luster - Vitreous
  • Cleavage/fracture - Imperfect in two lengthwise directions at close to right angles / uneven
  • Crystal habit/mode of occurrence - Prismatic (distinctive square cross section), tabular /granular
• Biotite


  A member of the mica group of silicates (sheet silicates), like chlorite and muscovite. It occurs in more geological environments than any of the other micas.
• Biotite


  • A common rock forming mineral, being present in at least some percentage in many igneous rocks (e.g. granite and rhyolite), and metamorphic rocks (e.g. schist, gneiss).
• Biotite


  • Chemical composition - K(Fe, Mg)3AlSi3O10(F, OH)2
  • Hardness - 2.5-3
  • Specific gravity - 2.9-3.4
  • Transparency - Transparent to translucent
  • Colour - Brown to black
  • Streak - Very pale brown
  • Lustre - Vitreous to pearly
  • Cleavage/fracture - Perfect in one direction producing thin sheets or flakes / uneven
  • Crystal habit/mode of occurrence - Tabular (sheets or flakes) / granular
• Calcite


  The only common non-silicate rock forming mineral, being instead calcium carbonate. It has two (2) refractive indices causing a significant double refraction effect.
• Calcite


  • Will fizz when dilute hydrochloric acid is placed on it. May be fluorescent, phosphorescent, thermoluminescent, and triboluminescent. An important rock forming mineral in sedimentary environments, being an essential component of limestones, and occurring in other sedimentary rocks. Also occurs in metamorphic and igneous rocks, and is common in hydrothermal environments. A common vein filling mineral in many rock types.
• Calcite


  • Chemical composition - CaCO3
  • Hardness - 3
  • Specific gravity - 2.7
  • Transparency - Transparent to translucent
  • Colour - Generally white or colourless, but also with light shades of yellow, orange, blue, pink, red, brown, green, black and grey
  • Streak - White
  • Lustre - Vitreous to resinous
  • Cleavage/fracture - Perfect in three directions at oblique angles / conchoidal
  • Crystal habit/mode of occurrence - Prismatic (rhombohedral crystals) / granular, massive
• Chlorite


  A member of the mica group of minerals (sheet silicates), like biotite and muscovite.