Types of Rocks and Their Formation. Igneous Rock Formation: Molten rock cools and becomes solid. Some igneous rocks form when magma below the surface.

Types of Rocksand

Their Formation

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

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