Rocks

Rock is the hard material that makes up the Earth’s crust, its hard “shell”. Rock lies beneath all natural soil layers—and everything else: city streets, a sandy beach...

Minerals A-Z

Minerals are naturally-occurring, solid, inorganic (non-living) substances that consist of chemical elements, such as silicon, oxygen, magnesium and others. Various combinations of...

Rock types A-Z

Igneous rocks

Igneous rocks are formed when magma, molten rock from beneath the Earth’s crust, rises, cools and solidifies. Intrusive igneous rock, such as granite, is formed when magma...

Metamorphic rocks

Metamorphic rocks are formed when rocks are subjected to such great pressure and heat that their mineral composition is altered. The original rocks may be sedimentary, igneous or...

Sedimentary rocks

Sedimentary rocks, such as sandstone and mudstone, are made from sand, gravel, mud and other fragments of rock that result from erosion. Limestone and chalk, also types of...

Gemstones

As rocks undergo metamorphism, pockets of minerals trapped inside them can be transformed into gemstones—rare and beautiful jewels. Different gemstones form at different levels...

Rocks A-Z