Classification of Rocks

By Hailey Schneider

Types of rocks

The major groups of rocks are defined: igneous, sedimentary, and metamorphic. Rocks are composed of one or more minerals.

Three Types of Rocks

Igneous Rock Basalt

  • Basalt forms outside of the earths surface from lava flow which causes the crystals to be smaller and to form slower
  • The crystal size is less than 1mm and the texture is fine
  • Basalt is vesicular
  • Basalt is a darker color, a higher density, and is mafic

Sedimentary Rock Conglomerate

  • The sedimentary rock conglomerate is inorganic
  • The grain size of this rock is pebbles, cobbles, and/or boulders embedded in sand, silt, and/or clay
  • The composition of this rock is mostly quartz, feldspar, and clay minerals; may contain fragments of other rocks and minerals
  • This rock is mainly rounded fragments

Metamorphic Rock Schist

  • The texture of this rock is foliated
  • The grain size of this rock is fine to medium
  • The composition of schist is mica, quartz, feldspar, amphibole, garnet, and pyroxene
  • The type of metamorphism is regional where heat and pressure increases
  • Platy mica crystals visible from metamorphism of clay or feldspars

The Rock Cycle

A cycle of processes undergone by rocks in or above the earths crust, involving igneous intrusion, uplift, erosion, transportation, deposition as sedimentary rock, metamorphism, remelting, and further igneous intrusion