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How to Tell the Difference Between the Three Rock Types

The three basic types of rocks are igneous, sedimentary and metamorphic. The differences in the three types arise because of how the rocks formed. Within each of the basic types of rock are more specific kinds. For example, limestone is a type of sedimentary rock, while marble is a type of metamorphic rock. Telling the difference in the three types can be done by a visual examination in most instances. Touching the rock and determining texture and strength are also keys to determining the type.

Things You'll Need

Nail
Glass of water
Pliers

Instructions

Examining the rock
- 1
  Look at your rock.
  
  If you can see pebbles or fossil imprints in the rock, it is of the sedimentary type. Fossil imprints will appear as the outline of leaves or insects.
  
  If the rock has layers that appear almost ribbon-like, or if you can see crystals in the rock, it is a metamorphic rock.
  
  If the rock is shiny and appears almost glass-like, it is an igneous rock.
- 2
  Run the pointed end of the nail over the rock, applying some pressure. If the rock is easily scratched, it is most likely that the rock is of the sedimentary type.
- 3
  Pour water over the rock. If the rock allows the water to pass through it, most likely the rock is of the sedimentary type. Both igneous and metamorphic are impermeable.
- 4
  Squeeze the rock with the pliers. Do not do this test unless you are willing to destroy the rock, however.
  
  If the rock crumbles easily, this means it is likely of the sedimentary type. Both igneous and metamorphic rocks are very strong and it is unlikely that you would be able to break them with pliers.

Rocks & Minerals