What are rocks and minerals, anyway?

Minerals -

a naturally occurring inorganic compound ("non-living material") possessing fairly definite physical properties and chemical composition

Rocks -

extensive mineral bodies composed of one or more minerals in varying proportions which form part of the earth's crust

How does a petrographer classify rocks?

INTO THREE GREAT GROUPS!

Sedimentary Rocks

Rocks weather and erode. Then they break down into smaller pieces of both rocks and minerals. These keep breaking down until a material called sediment exists.

Sediment can travel in water (ocean currents or rivers). Eventually, the sediment forms layers as it is deposited and buried. Over a long, long period of time these layers of sediment are "cemented" together to form new rocks known as sedimentary rocks!

Explore some sedimentary rocks!

Igneous Rocks

These rocks are formed when melted rock within the earth (magma) cools and then hardens.

Two basic types of Igneous Rocks exist: Intrusive & Extrusive

Intrusive -

form large masses within the earth

only appear at the earth's surface AFTER the rocks above them have eroded

Extrusive -

formed when magma erupts from a volcano in the form of lava & then cools

a volcano is an extrusive igneous formation

Want to know more about volcanoes -- then go! . . .

<-- Return to Grade 3 Science!