neroemerald.blogg.se - Define precipitate rock

The composition of the clasts depends on the composition of rock from which the clasts were derived, and on the degree of chemical weathering that the clasts have undergone. The size, angularity, sphericity, and sorting of clasts depends on the medium (water, ice, or wind) that transports the clasts and, in the case of water or wind, on both the velocity of the medium and the distance of transport.

This table provides common rock names specialists sometimes use other, more precise names based on more complex classiﬁcation schemes. With these characteristics in mind, we can distinguish among several common types of clastic sedimentary rocks. In some, the cement consists predominantly of quartz, whereas in others, it consists predominantly of calcite. Not all clastic sedimentary rocks have the same kind of cement.

Well-sorted sediment consists entirely of sediment of the same size, whereas poorly-sorted sediment contains a mixture of more than one clast size. Sorting of clasts indicates the degree to which the clasts in a rock are all the same size or include a variety of sizes. Sphericity, in contrast, refers to the degree to which the shape of a clast resembles a sphere. Angularity indicates the degree to which clasts have smooth or angular corners and edges. Clasts may be composed of rock fragments or individual mineral grains. Composition refers to the makeup of clasts in sedimentary rock. Names used for clast size, listed in order from coarsest to finest, are: boulder, cobble, pebble, sand, silt, and clay. Size refers to the diameter of fragments or grains making up a rock. Cement consists of minerals (commonly quartz or calcite) that precipitate from groundwater and fill the spaces between clasts. Compacted sediment may then be stuck together to make coherent sedimentary rock by the process of cementation.

First, once the sediment has been buried, pressure caused by the weight of overlying material squeezes out water and air that had been trapped between clasts, and clasts press together tightly, a process called compaction. The lithification of clastic sediment involves two steps.

Lithiﬁcation: Geologists refer to the transformation of loose sediment into solid rock as lithiﬁcation.

Sediment is deposited by ice when the ice melts. Sediment settles out of wind or moving water when these fluids slow, because as the velocity decreases, the fluid no longer has the ability to carry sediment.

Deposition: Deposition is the process by which sediment settles out of the transporting medium.

Strong winds can move sand and dust, but gentle breezes carry only dust. Very fast-moving, turbulent water can transport coarse fragments (cobbles and boulders), moderately fast-moving water can carry only sand and gravel, and slow-moving water carries only silt and clay. Solid ice can transport sediment of any size, regardless of how slowly the ice moves. The ability of a medium to carry sediment depends on its viscosity and velocity.

Transportation: Gravity, wind, water, or ice carry sediment.

Erosion involves abrasion, falling, plucking, scouring, and dissolution, and is caused by moving air, water, or ice.

Erosion: Erosion refers to the combination of processes that separate rock or regolith (surface debris) from its substrate.

Weathering: Detritus forms by disintegration of bedrock into separate grains due to physical and chemical weathering.