Rock

Rocks are naturally occurring mixtures of minerals, mineral matter, or organic materials. Three main types occur: sedimentary rocks, formed by weathering and mechanical sorting on the Earth's surface; metamorphic rocks, which are rocks that have been transformed by the effects of high temperature and pressure; and igneous rocks, derived from magma (for example, volcanic rocks ).

Did you know?

• Common sedimentary rocks include sandstone, limestone, and shale. These rocks often start as sediments carried in rivers and deposited in lakes and oceans. When buried, the sediments lose water and become cemented to form rock.
• Common metamorphic rocks include schist, marble, and gneiss. The sedimentary rock shale (formed mostly of clay sediments) when buried and heated to high temperatures (300-500°C) becomes transformed or metamorphosed into schist.
• Common volcanic (igneous rocks) are basalt, andesite, and rhyolite. When magmas crystallize deep underground they look different from volcanic rocks because they cool more slowly and, therefore, have larger crystals. Igneous rocks cooled beneath the Earth's surface are called intrusive rocks. The intrusive equivalents of basalt, andesite, and rhyolite are gabbro, diorite, and granite, respectively.