ROCK CLASSIFICATION all about the the rock cycle


Igneous rocks are formed from the solidification of molten rock material. There are two basic types.

Intrusive igneous rocks crystallize below Earth's surface, and the slow cooling that occurs there allows large crystals to form. Examples of intrusive igneous rocks are diorite, gabbro, granite, pegmatite, and peridotite.

Extrusive igneous rocks erupt onto the surface, where they cool quickly to form small crystals. Some cool so quickly that they form an amorphous glass. These rocks include andesite, basalt, obsidian, pumice, rhyolite, scoria, and tuff.


Sedimentary rocks are types of rock that are formed by the deposition and subsequent cementation of that material at the Earth's surface and within bodies of water. Sedimentation is the collective name for processes that cause mineral and/or organic particles (detritus) to settle in place.

There are three different types of Sedimentary Rocks.

Inorganic sedimentary rocks such as breccia, conglomerate, sandstone, silt-stone, and shale are formed from mechanical weathering debris.

Chemical sedimentary rocks, such as rock salt, iron ore, chert, flint, some dolomites, and some lime-stones, form when dissolved materials precipitate from solution.

Organic sedimentary rocks such as coal, some dolomites, and some lime-stones, form from the accumulation of plant or animal debris.

Where these Rocks are Found.

Sedimentary rocks form when mud and sand are deposited in layers on the Earth's surface. The layers are deposited in many environments including oceans, rivers and deserts. These layers of sand and mud are later buried. The weight of overlying layers compresses the mud and sand to form solid rock.


Metamorphic Rocks

Metamorphic rocks have been modified by heat, pressure, and chemical processes, usually while buried deep below Earth's surface. Exposure to these extreme conditions has altered the mineralogy, texture, and chemical composition of the rocks.

There are two basic types of metamorphic rocks.

Foliated metamorphic rocks such as gneiss, phyllite, schist, and slate have a layered or banded appearance that is produced by exposure to heat and directed pressure.

Non-foliated metamorphic rocks such as hornfels, marble, quartzite, and novaculite do not have a layered or banded appearance. Pictures and brief descriptions of some common types of metamorphic rocks are shown on this page.

Rocks can be metamorphosed simply by being at great depths below the Earth's surface,


Created with images by cluczkow - "rocks" • James St. John - "Obsidian" • Hat4Rain - "Sedimentary" • James St. John - "Clinker (Wasatch Formation, Lower Eocene; coal fire metamorphism at 19 ka, Late Pleistocene; large block at Interstate 90 west-bound hilltop rest area, east of Buffalo, Powder River Basin, Wyoming, USA) 6"

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