Rocks Wallpaper, #12631

In geology, rock is a naturally occurring aggregate of minerals and/or mineraloids. The Earth's lithosphere is made of rock. In general Rocks are of three types, namely, igneous, sedimentary, and metamorphic. Petrology is the scientific study of Rocks.Igneous Rocks are formed when molten magma cools and are divided into two main categories: plutonic rock and volcanic. Plutonic or intrusive Rocks result when magma cools and crystallizes slowly within the Earth's crust (example granite), while volcanic or extrusive Rocks result from magma reaching the surface either as lava or fragmental ejecta (examples pumice and basalt) .