Types of Rocks and Their Formation

Sedimentary Rock Formation: Layers of sediment are deposited at the bottom of seas and lakes. Over millions of years, the layers get compressed by the layers above. The salts that are present in the layers of sediment start to crystallize out as the water is squeezed out. These salts help to cement the particles together.

Sedimentary Rock Identification: Layers of sediment, easily scraped, and often crumble easily Often contain fossils which are fragments of animals or plants preserved within the rock. Only sedimentary rocks contain fossils.

Common Sedimentary Rock Sandstone

Common Sedimentary Rock Limestone

Metamorphic Rock Formation: Earth movements can push all types of rock deeper into the Earth. These rocks are then subjected to massive temperatures and pressures causing the crystalline structure and texture to change. They do not become liquid, but become molten.

Metamorphic Rock Identification: Hard rocks Foliated bands of fused minerals Crystalline structure with fused edges Movement of the Earth’s lithospheric plates cause the heating and squeezing conditions that form metamorphic rocks

Common Metamorphic Rock Slate

Common Metamorphic Rock Gneiss

Igneous Rock Formation: Molten rock cools and becomes solid. Some igneous rocks form when magma below the surface slowly cools and hardens. Some igneous rocks form when lava erupted from a volcano quickly cools.

Igneous Rock Identification: Igneous rocks contain minerals randomly arranged in crystals. If the rock has small crystals, this means that it had rapidly cooled. If the rock has large crystals, it means that it cooled slowly deep down within the crust without ever reaching the surface.

Common Igneous Rocks Granite

Common Igneous Rock Basalt