Most conglomerates are poorly sorted, and consist of a mixture of grain sizes ranging from sand to pebble. The schematic diagrams below represent poorly-sorted, moderately-sorted, and well-sorted sediments.
Other aspects of clastic sedimentary texture include the packing of the grains, the porosity of the rock, and the hardness of the rock as a whole. The packing of the grains applies only to poorly sorted sediments in which the finer clasts form a matrix around the coarser clasts. If the large grains are touching each other, the packing is said to be clast-supported. If the coarse grains are separate and not touching each other, with the finer-grained sediment between them, the packing is said to be matrix-supported.
The hardness of the rock refers to how easily it breaks apart. Shale is harder than claystone, for example. The common names of clastic sedimentary rocks—conglomerate, sandstone, siltstone, and shale—are based solely on grain size. However, there are more precise names within these broader categories that are based on clastic sediment features other than grain size.
Breccia is a clastic sedimentary rock distinguished from conglomerate by the angularity of its clasts.
A clastic sedimentary rock simply made of sand-sized grains qualifies as sandstone, regardless of what minerals the grains are made of. More complete names for various sandstones are based on their mineral composition. Some sandstones are made almost entirely of quartz.
Sandstone made virtually entirely of quartz is called arenite. Other sandstones have lots of feldspar mixed with quartz. Such sandstones are called arkose. In using the sedimentary rock classification table that accompanies this section, you will see that the clastic sedimentary rocks are classified on the basis of grain size.
Sandstones are rocks made of sand-size grains. Shale is layered sedimentary rock made of fine mud-size grains too small to see with the naked eye. The key to naming chemical sedimentary rocks is the minerals from which they are made.
For example, all limestones consist mostly of the mineral calcite. Rock salt is made of salt minerals such as halite. Gypsum rock is made of the mineral gypsum.
Chalcedony is made of microcrystalline quartz, quartz grains so tiny that they cannot be distinguished even with a standard optical microscope. Biochemical sedimentary rocks form with the help of past life. This can be in the form of fossils, shells or plant remains. For example, coal is made up of plant remains. Sedimentary rocks are used as building stones, although they are not as hard as igneous or metamorphic rocks.
Sedimentary rocks are used in construction. Sand and gravel are used to make concrete; they are also used in asphalt. Many economically valuable resources come from sedimentary rocks.
Iron ore and aluminum are two examples. Improve this page Learn More. Skip to main content. Home Igneous Rocks sedimentary. Igneous rock is formed through the cooling and solidification of magma or lava. Igneous rock may form with or without crystallization, either below the surface as intrusive plutonic rocks or on the surface as extrusive volcanic rocks. Sedimentary Rocks formed by the deposition of material at the Earth's surface and within bodies of water. While m afic Igneous rock, lesser content of silicon relative to felsic rocks, with predominance of mafic minerals pyroxenes, olivines and calcic plagioclase; these rocks example, basalt, gabbro are usually dark coloured, and have a higher density than felsic rocks.
Most sedimentary rocks contain either quartz especially siliciclastic rocks or calcite especially carbonate rocks. Furthermore, igneous rocks contain fossils very rarely, while sedimentary rocks are rich in fossils. In addition, igneous rocks are harder than sedimentary rocks.
Moreover, igneous rocks are light or dark coloured, while sedimentary rocks have great colour variety. The following infographic presents the further difference between igneous rocks and sedimentary rocks. Rocks are in three types as igneous rocks, sedimentary rocks, and metamorphic rocks. The key difference between igneous rocks and sedimentary rocks is their formation. Formation of igneous rocks is through magma, while lithification of existing rocks forms sedimentary rocks.
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Your email address will not be published. Figure Igneous Rock. Nonfoliated rocks can also form by metamorphism, which happens when magma comes in contact with the surrounding rock. Igneous Rocks Igneous rocks derived from the Latin word for fire are formed when molten hot material cools and solidifies. Igneous rocks can also be made a couple of different ways. When they are formed inside of the earth, they are called intrusive, or plutonic, igneous rocks.
Granite and diorite are examples of common intrusive rocks. They have a coarse texture with large mineral grains, indicating that they spent thousands or millions of years cooling down inside the earth, a time course that allowed large mineral crystals to grow.
Alternatively, rocks like basalt and obsidian have very small grains and a relatively fine texture. This happens because when magma erupts into lava, it cools more quickly than it would if it stayed inside the earth, giving crystals less time to form. Obsidian cools into volcanic glass so quickly when ejected that the grains are impossible to see with the naked eye.
This happens when the ejected magma still has gases inside of it so when it cools, the gas bubbles are trapped and end up giving the rock a bubbly texture. An example of this would be pumice. Any rock type can become any other. The audio, illustrations, photos, and videos are credited beneath the media asset, except for promotional images, which generally link to another page that contains the media credit. The Rights Holder for media is the person or group credited.
Tyson Brown, National Geographic Society. National Geographic Society.
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