Sedimentary Rocks Properties

Sedimentary Rocks:

They are rocks that are formed on or near the Earth's surface by the accumulation and lithification of rock sediments, or by the leaching of chemicals from solutions at normal surface temperatures. Sedimentary rocks are the most common on the outer surface of the lithosphere, where sedimentary rocks are produced through weathering, erosion, transportation, sedimentation, and chemical decomposition processes that occur when rocks on the Earth's surface are exposed to atmospheric factors and weather elements.

Sedimentary Rocks Properties

Physical Properties

• Porosity and Permeability: They are among the most important basic physical properties in relation to the storage and transport of fluids, as sedimentary rocks retain oil and petroleum materials due to their porosity. Researchers needed to conduct accurate studies on sedimentary rocks for effective development and management, and to know the future production of oil fields by determining the amount of porosity and permeability, as well as the chemical composition with the greatest possible accuracy.

• Texture: It is the form of arrangement of the grains and separate particles that make up sedimentary rocks. Geologists and researchers have found, through studying the composition of rocks, that there are two types of texture that make up sedimentary rocks: the clastic texture and the non-crystalline texture. The crystalline texture in non-carbonate chemical sedimentary rocks is formed in the form of separate mineral grains that form an interlocking arrangement. The size of the crystal and the change in the crystalline texture depend on the rate of rainfall.

• Particle size: The size of the particles is an important feature of sedimentary rocks because it provides information about the conditions of transport and deposition of sediments and provides some evidence about the most important geological events that occurred in the sedimentary site. It may be difficult to determine the sizes of the separate particles that make up sedimentary rocks, especially if the rocks are compressed and fossilized. The size of the particulate materials that make up sediments and sedimentary rocks is measured by measuring the weight of the particles that accumulate in wire mesh sieves, or by determining the rate at which particles of different diameters accumulate in a glass cylinder filled with water.

Characteristics of mineral and geochemical composition

Chemical compounds are formed at the depositional site in response to geochemical processes, where they are formed by chemical weathering processes and transported from the weathering site to the point of deposition as solutions. Clay minerals are abundant in sedimentary rocks and were produced at the weathering site by partial decomposition of minerals such as feldspar. Examples of clay minerals are: kaolinite, montmorillonite, vermiculite, and chlorite.

Types of Sedimentary Rocks

Sedimentary rocks are formed by weathering processes that occur on the surface of the Earth, as there are two types of weathering: physical (mechanical) weathering, and chemical weathering, and due to the great difference between them, they form sediments and sedimentary rocks of different types, and the following are two types of sedimentary rocks:

Catalytic sedimentary rocks

• They are rocks that consist of rock remains and mineral grains of varying sizes, in addition to clay, silt, sand, gravel, and paved materials, as these blocks are transported by gravity, mudflows, running water, glaciers, and wind, and eventually settle in different places such as river deltas, continental margins, and sand dunes. The type of rock formed also depends on the size of the transported blocks, as sandstone is made up of coarse gravel, while mudstone is made up of silt and clay.

  
  

• Chemical sedimentary rocks Chemical sedimentary rocks are formed by the chemical and organic precipitation of dissolved products of chemical weathering that are transported from the weathering site by water and transport and deposition processes. Chemical sedimentary rocks are formed from limestone and chemical elements dissolved from surrounding rocks such as calcium carbonate. Examples of chemical sedimentary rocks include limestone, sediments resulting from the evaporation of halite, gypsum, and anhydrite.

Materials that make up sedimentary rocks

Sedimentary rocks are formed by the deposition of ancient rock and mineral materials close to the surface of the earth or under water. These materials are usually deposited in horizontal layers. The materials that make up sedimentary rocks may contain different components such as:

• Stone or mineral residues resulting from the natural erosion of various types of rocks that existed previously, due to weathering, erosion, transport, and deposition processes.

• Chemical sediments formed by the continuous deposition of chemical elements of surrounding rocks. Sediments of organic matter containing the remains of dead plants and organisms, and exposed to pressure and heat.