Shale forms from the pressure of layers of sediment compressing bits of silt that settle into the clay on the bottom of bodies of water. The compressed clay and silt become shale over time. Shale is a sedimentary rock.Continue Reading
Shale starts with bits of rock that erode off of larger rocks from contact with moving water and the weather. Very fine particles of feldspar, quartz, mica, pyrite and other minerals settle to the bottom of still bodies of water, such as swamplands, deep parts of the ocean and deep, still lakes. The fine rock particles mix with decaying organic matter into a mud. Because weathering is a continual process, new layers are always building up. The top layers press on the bottom layers with more and more pressure. When enough pressure builds up, the bottom layers become rock through a process called lithification. Lithification causes the thin layers that are characteristic of shale.
Shale is a soft rock that breaks easily. The color varies depending on the exact minerals that formed the shale. Red, green and black are some color variations. Geologists classify shale as a claystone due to the small size of the particles that form the rock. Shale is a common rock that makes up much of Earth's crust.Learn more about Geology
Clay most commonly forms due to erosion or weathering; both methods involve rocks coming into contact with something, such as air or water, to form the clay from existing minerals on the ground. It is common for clay to form in specific geological environments, such as where there are volcanic deposits, marine sediments or soil horizons.Full Answer >
Shale, marble, mudstone, slate and well-packed sandstone are all examples of impermeable rocks, which means that water cannot easily pass through them. A large number of metamorphic and igneous rocks are impermeable, as long as they are not fractured.Full Answer >
According to the National Park Service, sedimentary rock forms when mud and sand are deposited into layers on the earth’s surface and later buried. The buried mud and sand is compacted by the weight of the overlying layers of earth until they harden and form solid rock.Full Answer >
Magnetite forms in small quantities interspersed with many iron-rich minerals, but only forms bodies of crystals on its own when mafic magma, a very liquid magma laden with heavy elements, cools sufficiently slowly for individual crystals to clump together. Magnetite can also form during metamorphism of impure iron-rich limestone.Full Answer >