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 - magma & lava

• mafic to felsic (or acidic)
  • dark basalt (Hawaii)
  • intermediate andesite (Mt. Lassen)
  • lighter rhyolite (Idaho, Sierra Nevada)
    
    
  
  
• intrusive - "plutonic" rocks formed deep beneath Earth’s surface
  • lighter granite (Sierra Nevada)
  • dark gabbro (Penryn, CA)
    
    
    • coarse crystals
      • cools much slower beneath surface
  
  
• volcanic / extrusive - volcanic events
  • Cascades Mtns of Pacific Northwest
    
    
    • little or no crystals
      • cools rapidly at surface
        
        
• "jointed" igneous rocks
  • basalt - columnar jointing (Devil's Postpile)
  • granite - exfoliations (Yosemite domes)
    
    

Sedimentary rocks

• stratification - "strata" or layers stacked upon one another
  
  • Grand Canyon N.P.
  • Transverse Range, CA
  • Zion N.P. - cross-bedding - former sand dunes
    
    
• sediments compacted by pressure
  • removing air spaces and pores
  • cementation from silicon dioxide, calcium carbonate, iron oxide
    
    
• visible in southwestern landscapes
• Zion N.P., Arches N.P., Capitol Reef.
  
  

Sedimentary categories

• clastics / detrital - broken rock fragments glued together
  • conglomerates, sandstone, and shale
    
    
• organic rocks - remains of plants and animals
  • coal (decayed plants)
  • limestone - calcium from skeletal remains
    • chalk cliffs
      
      
• chemical (precipitates) - chemical solutions
  • limestone, gypsum,
  • halite (salt), borates (used for detergents)
    
    

Metamorphic - "change shape"

• characterized by foliation and hardness
  • enormous heat and pressure change structure of rock
  • harder and more compact, resistant to erosion
    
    
• sedimentary and igneous changed
  • limestone to marble
  • shale to slate
  • granite to gneiss
    
    
• metamorphism found in Gold country
  • Rock Table - many others
    
    • Local Rock Hunt

Rock Cycle - recycled rocks

• how do hard rock become sediment?
• how do sediments become molten igneous rock?
• how do igneous become metamorphic rock?
  
  

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 rock)
    • N. America, Florida, Yucatan Peninsula