Classification of Rocks

all rocks fit into three (3) major categories: Igneous - "fire rocks" from inside Earth Sedimentary - sediments cemented together Metamorphic - recycled and changed

Igneous rocks -

• mafic to felsic (or acidic) -
  
  
  
  
  
  
• Plutonic / intrusive rocks -
  
  
  
  
  
  
• Volcanic / extrusive rocks -
  
  
  
  
  
  
• "jointed" igneous rocks
  • basalt - columnar jointing (Devil's Postpile)
  • granite - exfoliations (Yosemite domes)
    
    

Sedimentary rocks - sediments cemented together

• stratification - "strata" or layers stacked upon one another
  
  
  
  
• sediments compacted by pressure
  
  
  
  
• visible in southwestern landscapes

• Zion N.P., Arches N.P., Capitol Reef
  
  

Sedimentary categories

• clastics / detrital - broken rock fragments glued back together
  • conglomerates, sandstone, and shale (compressed clay)
    
    
    
• organic rocks -
  
  
  
• chemical (precipitates) -
  
  
  

Metamorphic rocks - "change shape"

• characterized by foliation and hardness
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• sedimentary and igneous changed
  • limestone to marble
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• metamorphism found in Gold country
  
  

Rock Cycle

• all rocks eventually end up being recycled
  
  
  

Isostasy and crustal rebound

• major uplift and deformation of large landmasses
  • well after plate tectonics
• mountains continue to rise; float on denser asthenosphere
  • lifted primarily by removal of weight & mass
    • ice caps, oceans, or sediments