Theme of the Day:

• Geologic Processes and the Rock Cycle
• Rock Types
• Rocks & Minerals: Hands On

Geologic Processes and the Rock Cycle

• Geologic Materials
  • Magma - molten rocks
  • Igneous Rocks - crystallized from a magma
  • Sediment - rock and mineral fragments produced by weathering
  • Sedimentary Rocks - reconstituted from weathered rock fragments or chemicals - usually deposited by wind, water, or ice
  • Metamorphic Rocks - pre-existing rock that has undergone changes in the solid state as a result of elevated pressure, temperature, or fluids
• Transitions within the Rock Cycle
  • Magma cools and crystallizes (solidifies) to form igneous rocks - ex. Hawaiian lava
  • Weathering is the physical or chemical breakdown of a rock (any type) and results in the formation of a sediment
  • Physical sediments can be lithified by compaction and cementation into sedimentary rocks - chemical sediments can precipitate from solutions to form sedimentary rocks
  • Igneous or sedimentary rocks can undergo metamorphism (solid state change) at high T or P or in the presence of fluids
  • Metamorphic rocks may melt to form magmas under conditions of increasing T, decreasing P, or increased fluids
• Rock Origins in Relation to Driving Forces: Internal and External

• Rocks are generally made up of one or more minerals.
• Some common rock-forming minerals.
• Igneous Rocks
  • Form by cooling and crystallization of magmas
  • Usually tight, interlocking crystals, generally silicate minerals
  • Crystal size (grain size) varies based on cooling rate - fast cooling = fine-grained, slow cooling = coarse-grained
  • Composition (chemical, mineralogical) varies from mafic to felsic
• Sedimentary Rocks
  • Form at or near the surface of Earth by reconstitution (lithification) of fragments or chemical constituents that result from the weathering process
  • Usually formed in stratified layers that obey Steno's Laws (Original Horizontality, Lateral Continuity, Superposition)
  • Clastic, Chemical, and Organic varieties
  • Often record important information about depositional environments
• Metamorphic Rocks
  • Rocks that have undergone changes (textural, mineralogical) in the solid state (no melting involved)
  • Often preserve information about their protolith (pre-metamorphic rock type) and the pressure and temperature conditions under which they equilibrated