The crust is underlain by the mantle. The oceanic crust of the Earth is different from its continental crust. The crust and underlying relatively rigid mantle make up the lithosphere. Related Stories. And researchers It Depends on Where You Live. Print Email Share.
Most Popular Stories. The inner core spins at a different speed than the rest of the planet. This is thought to cause Earth's magnetic field. When charged particles from the solar wind collide with air molecules above Earth's magnetic poles, it causes the air molecules to glow, causing the auroras — the northern and southern lights.
To better understand Earth's composition and history, geologists sometimes compare our planet to other rocky planets in our solar system. Venus is a similar size to Earth and a little bit closer to the sun, while Mars is only about half the size of Earth.
Although several spacecraft have been sent to Venus and Mars, we know very little about their interiors — yet. The InSight mission is expected to launch in to do a deep drill into the surface of Mars and yield more information about the interior.
Some planned rovers also carry lengthy drills, such as the ExoMars rover that launches in Venus has an extremely thick atmosphere that blocks visible light from reaching the surface, which means it requires radar to look at the surface. The surface appears fresh and young — no more than million years old — due to the amount of volcanic activity on Venus' hellishly hot surface.
While Venus likely has a crust, mantle and core similar to Earth, its magnetic field is very weak compared to Earth's. That may be because the core spins sluggishly to generate the magnetic field, or because there is no core at all. Mars is a cold planet whose atmosphere is not thick enough to let liquid water flow at the surface although briny water is a possibility. It has a crust covered by dust; it's believed the crust is solid, with no plate tectonics. This allowed Mars to build up huge volcanoes on its surface, such as Olympus Mons.
It is pretty common rock type associated with subduction zone volcanism but not as widespread as basalt. By the way, the average composition of the continental crust is that of andesite. Hence, we believe that it gives us a hint how the continental crust formed.
It is subduction zone volcanism that creates lava intermediate in composition that is less dense than basaltic rocks of the oceanic crust and is therefore not able to dive back into the mantle. So, the continental crust is not recycled by the conveyor belt of the oceanic crust and can only grow bigger and bigger as time goes by.
Rhyolite is a volcanic equivalent of granite. The sample from Scotland is 8 cm in width. Gabbro is a mafic intrusive rock. The sample from Cyprus from the Troodos ophiolite which represents former oceanic crust is 7 cm in width. Basalt is a volcanic equivalent of gabbro. The sample from Northern Ireland is 8 cm in width. Andesite is a common volcanic rock which is intermediate in composition between mafic and felsic rocks.
White mineral is plagioclase. The width of the sample from Santorini is 7 cm. This rock type was once sandstone, but it got buried so deep that quartz grains fused together to form a tough metamorphic rock known as quartzite. The sample is from Ireland. Marble is a metamorphosed limestone. It is composed of calcite. The outcrop is located in Karelia, Russia. Schist is a strongly foliated metamorphic rock, most likely metamorphosed mudstone. Photo taken in Scotland.
A hand sample of schist from Spain. Width of sample 9 cm. Chlorite schist is a metamorphosed mafic igneous rock that is rich in iron-bearing green sheet silicate mineral chlorite that gives slaty cleavage to the rock.
Width of sample 13 cm. Gneiss is a very common metamorphic rock. Perhaps up to one fifth of the crust is composed of gneissic rocks. Karelia, Russia. This specimen has a composition of an ordinary granite: pink K-feldspar, gray quartz, and black biotite. Marshall, Clare P. Composition of the crust. October 28, at Mario Fragata. April 22, at Folds at Loughshinny ». Recent Posts. Composition of the crust The crust is compositionally distinct outermost rocky layer of the Earth.
Chemical elements in the crust The most common chemical elements in the crust are oxygen These figures vary among different studies because we really have no way to know for sure. Element Mass percent Common minerals Common rocks Oxygen.
Silicates, oxides, etc. Oxygen is extremely widespread in the crust and very reactive as well. Volumetrically insignificant part of all the minerals contain no oxygen. Almost every common rock type contains oxygen. Only sulfide ore bodies and evaporite beds are almost free of oxygen, but they are volumetrically relatively insignificant. Silicon has its very own large group of minerals known as silicates. Silicon and oxygen are the two most common chemical elements in the crust that also happen to like each others company very much.
There is not a single common non-silicate mineral that contains silicon — silicon always combines with oxygen. Silicate minerals are the building blocks of most common rock types basalt , granite , schist, gneiss , sandstone, etc. Carbonate rocks limestone, dolomite rock and evaporites gypsum rock, rock salt are notable exceptions. They do not contain silicon if they are pure. Opaque ore minerals oxides and sulfides are frequent minor components of most rock types.
They are also free of silicon. Very widespread in silicate minerals feldspar , clay minerals, mica. Aluminum hydroxides boehmite, diaspore, gibbsite are economically important as aluminum ore minerals. Hence, aluminum is extremely widespread as well. It is usually not very concentrated in silicate minerals, though. Aluminum has been extracted from silicate rocks very rarely. Bauxite which is aluminum-rich laterite formed in humid hot areas contains aluminum hydroxides and is primarily mined for aluminum.
Aluminum in bauxite is a residue of chemical weathering of silicate rocks. Iron is a widespread element in minerals. Notable iron-rich silicate minerals are pyroxenes, amphiboles , olivine , black mica biotite , garnet , etc. Iron is also an important element in sedimentary rocks. It is just like aluminum hard to dissolve and carry away with water. Iron is common in lateritic soil and forms rust-colored iron oxide mineral hematite.
Hematite is responsible for the red coloration of many minerals and rock types. Iron oxide magnetite is common as an accessory mineral in metamorphic and igneous rocks. Iron sulfide pyrite is the most common sulfide mineral.
Iron also occurs in carbonates siderite , ankerite , clay minerals glauconite , chlorite. Iron is a strong chromophore element, it gives dark coloration to its host minerals. This is why most pyroxenes and amphiboles are black. Iron is actually the single most abundant chemical element in the whole of Earth, but most of it is in the core. Basalt, gabbro , amphibolite, greenschist , etc. There is a large number of rock types that contain significant amount of iron, but most of the iron mined comes from metamorphosed sedimentary rocks known as BIF banded iron formation.
Calcium is also very widespread. The most important pyroxenes and amphiboles augite and hornblende contain calcium. Calcium occurs in many other silicate minerals like garnet, epidote , wollastonite , titanite, etc. Calcium is a constituent of calcite which is very important mineral chiefly in sedimentary environments.
Calcium phosphate apatite is a common mineral as well.
0コメント