Rocks and minerals

• Rock Cycle


  1. Erosion

  2. Transport

  3. Deposition

  4. Diagenesis

  5. Crystallization

  6. Melting

  7. Pressure and Temperature
• Igneous Rock


  Formed through the cooling and solidification of magma
• Weathering


  The process of decomposing, breaking up, or changing the physical and chemical composition of rocks
• The shells crumble and finally become sedimentary rocks
• Other sedimentary rocks may form from the remains of plants or animals interred with the sediments
• Types of rocks


  • Igneous
  • Sedimentary
  • Metamorphic
• Igneous rocks


  • Formed when magma (melted materials under the Earth's crust) cools and hardens
  • May have small mineral crystals (e.g. basalt, felsite)
  • Can form glasslike solids when cooled quickly (e.g. obsidian)
  • Can have gas bubbles when cooled rapidly (e.g. pumice)
• Sedimentary rocks


  • Formed from deposits at the bottom of the ocean (gravel, sand, clay, plant/animal matter)
  • Cemented together by minerals in the water
  • Often have a banded appearance due to differences in color, grain, and size between layers
  • Can contain fossils or remains of plants/animals
• Metamorphic rocks


  • Formed when sedimentary or igneous rocks are subjected to high pressure and temperature deep beneath the Earth's surface
• Rock cycle


  Continuous change from magma to rock and back to magma
• The heat from the Earth's interior causes materials under the crust to melt, forming magma and lava
• When lava cools, it hardens and forms igneous rocks
• Igneous comes from a Latin word meaning "fire"
• Obsidian is an igneous rock that cooled quickly, forming a glasslike solid with no crystals
• Pumice is an obsidian that cooled so rapidly it has gas bubbles trapped in it, making it float on water
• Sedimentary rocks are formed from deposits at the bottom of the ocean, cemented together by minerals
• Sedimentary rocks often have a banded appearance due to differences between layers
• Shale is a sedimentary rock made up of tightly packed layers of clay and limestone from shells of dead animals
• Metamorphic rocks are formed when sedimentary or igneous rocks are subjected to high pressure and temperature deep beneath the Earth's surface
• The name "metamorphic" comes from a Greek word meaning "to change"
• Crystal form


  Definite chemical composition that forms a definite structure which crystallizes into a specific crystal form
• Crystal habit


  The outward appearance of the mineral's crystal form
• Crystal habit descriptions


  • granular
  • tabular
  • dendritic
  • acicular
  • massive
  • reniform
  • drusy
  • encrusting
• Cleavage


  The tendency of a mineral to break along planes of weakness
• Cleavage quality


  • excellent
  • good
  • poor
  • absent
• Minerals with excellent cleavage will break into smooth, flat, parallel surfaces
• A good cleavage will result in small, smooth, steplike flat surfaces
• Cleavage surfaces are difficult to identify in minerals with poor cleavage
• Minerals that do not have cleavage will fracture either in an irregular manner or as conchoidal fracture (smooth, curved surfaces)
• Luster


  The appearance of light as it is reflected off a mineral's surface
• Nonmetallic mineral lusters


  • vitreous (like glass)
  • resinous (like resin)
  • pearlescent
  • silky
  • greasy
  • earthy
  • dull
• Color


  The most obvious mineral property, but not a reliable feature for identifying minerals as it can be altered by chemical impurities
• Quartz is colorless but slight impurities can produce a variety of colors, such as white (like in milky quartz), yellow (like in citrine), purple (like in amethyst), or black (like in smoky quartz)
• Streak


  The color of a mineral in its powdered form, can be identified using a streak plate
• Hardness


  A measurement of the strength of the chemical bonds in a mineral's structure, can be measured by scratching it with another mineral or a reference material with known hardness
• Mohs scale of hardness

  • Diamond (10)
  • Corundum (9)
  • Topaz (8)
  • Quartz (7)
  • Orthoclase (6)
  • Apatite (5)
  • Fluorite (4)
  • Calcite (3)
  • Gypsum (2)
  • Talc (1)
• The soft, dull, dark gray-to-black, common mineral graphite has the same chemical composition as the brilliant, colorless, rare, and hardest mineral diamond, both are composed purely of carbon
• Diamonds crystallize at very high pressure and temperature conditions, forming strong giant covalent bonds under an isometric system, while graphite forms at lower temperature and pressure under a hexagonal system
• Density


  Specific gravity, the weight of a mineral relative to the weight of an equal volume of water
• Most common minerals have a specific gravity of 2.7, while gold has 19