Sedimentary rocks cover approximately 75% of the earth’s surface. It is important to know as much as we can about the characteristics of these rocks because when humans interacting and alter with earth materials it is most likely going to be a sedimentary rock. When we engage in construction projects, dispose of waste materials, look for a water supply, or extract mineral resources, is it most likely going to be sedimentary rock.
These are formed from the products of the weathering of preexisiting rocks. When these sediments are compacted by pressure of overlying material or cemented together by precipitation of mineral matter between the particles, new rock is formed. Sedimentary rocks may also be formed from the accumulation of organic materials and from chemical precipitation of mineral matter from water.
These rocks can be formed from a process called mechanical weathering where the breakdown of rock into particles without producing a chemical change within the minerals composition. Ice is the biggest and most important cause of mechanical weathering. The force exerted by the expansion is sufficient to widen cracks and break off pieces of rock. Heating and cooling of the rock, and the resulting expansion and contraction, also aids the process. Mechanical weathering contributes further to the breakdown of rock by increasing the surface area exposed to chemical agents.
Another process that aids in the breakdown of rock is chemical weathering. In this process the minerals within the rock are changed into particles that can be easily carried away. The minerals in igneous rocks may be unstable under normal atmospheric conditions, those formed at higher temperatures being more readily attacked than those which formed at lower temperatures. Igneous rocks are commonly attacked by water, particularly acid or alkaline solutions, and all of the common igneous rock forming minerals are changed in this way into clay minerals and chemicals in solution.
Sedimentary rocks are of great economic significance. They can be used as building materials, aggregates, glass, ceramic products, and the fossil fuels, as well as some metallic mineral deposits. Limestone may be highly soluble, therefore, unsuitable for construction projects. The coarser clastic rocks, like, conglomerate and sandstone, are generally porous and permeable and as a result are the source of abundant groundwater. These rocks are useful in construction projects because they posses good support strength.