Rocks

Rocks

Bare rock faces in the mountainsBare rock faces in the mountains 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, even the ocean. Of course, bare rock lies at the surface itself in many places, such as at the tops of mountains or on sea cliffs. Rocks are stony masses made up from minerals. Minerals, in turn, consist of chemical elements, such as silicon, oxygen or magnesium.

A close up view of sandA close up view of sand

Quartz crystalsQuartz crystals

Minerals

There are thousands of different minerals, but a very few kinds (feldspar, mica and quartz, for example) are found in nearly all the Earth’s rocks. Various combinations of minerals make up different types of rocks. For example, the rock sandstone consists mainly of grains of sand pressed and cemented together. Sand is made mainly of the minerals quartz and feldspar. Quartz consists of the chemical elements silicon and oxygen; feldspar is composed of a variety of elements.

The oldest rocks on Earth are found in the Canadian Shield in the Northwest Territories. There, gneiss, a metamorphic rock which forms the core of an ancient mountain chain, has been dated to more than 4 billion years old.

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