1. sedimentary rocks
   1. clastic
      1. shale
      2. sandstone
   2. chemical
      1. bituminous coal
      2. chalk
      3. limestone
2. igneous rocks
   1. extrusive
      1. pumice
      2. rhyolite
      3. obsidian
      4. basalt
   2. intrusive
      1. granite
3. metamorphic rocks
   1. foliated
      1. regional metamorphism
         1. gneiss
         2. schist
   2. nofoliated
      1. contact metamorphism
         1. slate
         2. marble
         3. anthracite coal