Living things also help form soil. Once rock is weathered into smaller particles, microorganisms and small plants begin to establish themselves there. The microorganisms’ metabolisms release carbon dioxide which readily dissolves in water, forming additional amounts of carbonic acid. The weathering process continues, creating finer particles of new minerals. Below are some examples.
This is the decomposition of rocks due to chemical reactions occurring between the minerals in rocks and the environment. The examples below illustrate chemical weathering.
Water
Water, and many chemical compounds found in water, is the main agent of chemical weathering. Feldspar, one of the most abundant rock-forming minerals, chemically reacts with water and water-soluble compounds to form clay.
Sometimes called mechanical weathering, physical weathering is the process that breaks rocks apart without changing their chemical composition. These examples illustrate physical weathering:
Swiftly moving water
Rapidly moving water can lift, for short periods of time, rocks from the stream bottom. When these rocks drop, they collide with other rocks, breaking tiny pieces off.
Rock is either broken into smaller particles (disintegration-physical weathering) or altered into other kinds of minerals (decomposition - chemical weathering). Although these processes do not occur in isolation, it is easier to understand them by considering them separately.
Metamorphic rocks are rocks that have become changed by intense heat or pressure while forming. In the very hot and pressured conditions deep inside the Earth’s crust, both sedimentary and igneous rocks can be changed into metamorphic rock. In certain conditions these rocks cool and crystallize usually into bands of crystals. Later they can become exposed on Earth’s surface. One way to tell if a rock sample is metamorphic is to see if the crystals within it are arranged in bands.
Rocks are mixtures of one or more minerals. Just like the apples, butter, flour, and sugar are the ingredients of apple pie, minerals like quartz, mica, and feldspar are the ingredients of an igneous (from the Latin word for fire) rock called granite.
Sediment is made up of solid, loose pieces of rocks (in the form of sand, silt, clay, and gravel), or the remains of living things found at the surface of the Earth. Sediment is material that has been eroded and deposited by wind, running water, waves, and ice.
Rocks are mixtures of one or more minerals. Sedimentary rocks are made of solid, loose pieces of rocks (in the form of sand, silt, clay, and gravel), or the remains of living things found at the surface of the Earth, that over a very long period of time, has become compacted and cemented into sedimentary rock. Igneous rocks come from melted rock material, or magma, that lies beneath Earth’s surface. Metamorphic rocks are rocks that have become changed by intense heat or pressure while forming.
