11.9: Non-Clastic Sedimentary Rocks
How Do I Recognize a Non-Clastic Sedimentary Rock?
If the sedimentary rock is the product of chemical weathering, it will be referred to as non-clastic sedimentary rock Links to an external site., an all-inclusive term which covers sedimentary rocks produced via chemical, biochemical or organic processes. In a non-clastic rock, the classification is based primarily on the composition of the material and how it developed.
Chemical and Biochemical Sedimentary Rocks
In general, chemical sedimentary rocks typically have a crystalline appearance and form through the inorganic precipitation of minerals from a fluid. If the ions present within a fluid (water) become very concentrated, either by the addition of more ions or the removal of water (by freezing or evaporation), then crystals begin to form. In this case, identification of the type of sedimentary rocks is based on the minerals present.
In biochemical rocks, organisms typically facilitate the precipitation of these minerals from water. An example of biochemical precipitation is the formation of skeletal minerals in many organisms: from starfish and clams that grow calcite, to sponges that grow silica-based material, to humans that have bones and teeth made of hydroxyapatite. In many cases, it is hard to differentiate whether a mineral was formed organically or inorganically. Organic sedimentary rocks are those formed mostly from carbon-based organic material produced by ancient life.
Carbonate Sedimentary Rocks
Carbonates are one of the most important groups of sedimentary rocks. They can result in distinctive landscapes, called karst topography (more on this in Groundwater) and human hazards like sinkholes.