Igneous Rocks

Extrusive rocks are types of igneous rocks that are formed when volcanic materials erupt, cool, and then crystallizes on Earth's surface.

Basalt is a type of extrusive rock. This rock has no crystals that are visable to the unaided eye. It also has a low silica content.

Intrusive rocks are igneous rocks that form as magma cools underground.

Granite is a type of intrusive rock. It has lots of crystals that are visable to the naked eye and has a high silica content.

Composition:

Igneous rocks are partly classified by their silica content. Lighter colored rocks contain greater amounts of silica, while darker rocks contain less silica and more magnesium and iron.

Sedimentary Rocks

Sediment is made when air or water can cause rocks to break apart, dissolve, or form new minerals. This process is called weathering. Sediment can be transported by water, glacial ice, gravity, or wind.

Compaction is a process is which the weight from the sediment layers forces out fluids and decreases the space between grains.

Cementation is a process in which minerals dissolved in water crystallize between sediment grains.

Clastic rocks is a classification of sedimentary rock. These types of rocks are made up of broken pieces of minerals and rock fragments. For example, Conglomerate (left) and Breccia (right) are clastic rocks.

Chemical rocks is also a classification of sedimentary rock. These rocks form when minerals crystallize directly from water. For example, chemical limestone (left) and rock salt (right) are chemical rocks.

Biochemical rock is a classification of sedimentary rock. These rocks are formed by organisms or contains the remains of organisms. For example, chert (left) and coal (right) are biochemical rocks.

Biochemical rock is a classification of sedimentary rock that is formed by organisms or contains the remains of organisms. For example, chert (left) and coal (right) are biochemical rocks.