How to Know how Rocks are Formed

When looking at a rock, a person might ask "how was that rock formed?" In geology, there are three main types of rocks and rock formation - igneous, sedimentary, and metamorphic - each formed in a different way through the rock cycle. This brief article will help you know how each of these three main types of rocks are formed.

Difficulty: Easy

Instructions

1. 
   Kilauea in Hawaii

   Igneous Rocks - These types of rocks are formed out of molten rock material (magma) ejected from the earth's interior onto the earth's surface (lava) and cools, or when the molten material pushes up below the surface and cools just underneath. Igneous rocks are common in volcanically active areas. The Hawaiian Islands contain examples of relatively young igneous rock.

2. 
   Grand Canyon in Arizona

   Sedimentary Rocks - These types of rocks are formed when small pieces of rock and often organic material as well are cemented together in layers over long periods of time. The Grand Canyon contains excellent examples of sedimentary rock layers, representing over two billion years of geologic history.

3. 
   Banded Metamorphic Rock in Nevada

   Metamorphic Rocks - These types of rocks are formed when preexisting sedimentary or igneous rocks are subjected to extreme pressures - such as stretching, smashing, and high temperatures - and subsequently their appearance and mineral composition is changed. Many mountain ranges contain good examples of metamorphic rock due to the high pressures endured by the rock during mountain building processes.