What is chemical weathering? Contrast this set of processes to physical weathering.

Physical weathering, or mechanical weathering, is one of nature's fundamental processes affecting the Earth's crust. It's the breaking down of rocks and minerals into smaller pieces without altering their chemical composition. Imagine it as a sugar cube breaking into granules—its sweet nature hasn't changed, just its size.

Physical weathering is driven by a variety of environmental factors. Temperature fluctuations, for instance, can cause expansion and contraction in rocks, leading to cracks. Similarly, the freeze-thaw cycle is notable where water seeps into cracks, freezes and then expands, thereby widening fractures. Over time, with repeated cycles, rocks can split and fragment.

Biological activity also plays a role. Plant roots can grow into tiny crevices, exerting pressure that splits rock. Furthermore, burrowing animals and insects churn the ground, fostering physical weathering. Even humans contribute through construction and agricultural activities. Although seemingly less dramatic than chemical processes, physical weathering is a crucial precursor that increases the surface area exposed to chemical agents, thereby accelerating chemical weathering.

Rock disintegration is a facet of physical weathering that directly pertains to the breaking down of solid rock into smaller fragments. This process can occur via a plethora of mechanisms, each with its distinct modus operandi. Apart from temperature and biological influences mentioned earlier, other agents include water, wind, and gravity.

Crystallization Forces

Salt crystals forming from evaporated water can exert significant outward pressure on the surrounding rock, leading to disintegration. This is quite common in arid and coastal regions.

Physical Abrasion

Wind and water can carry sand, silt, and other particles that scour rock surfaces, akin to natural sandblasting. This abrades and diminishes rock structures over time.

The result of rock disintegration is a range of sediments, from boulders to sand grains. These materials are further acted upon by different earth processes, transported by water and wind, and ultimately contribute to soil formation, landscapes and various geological features.

Mineral composition is the key factor determining how a rock will undergo both chemical and physical weathering. Minerals are naturally occurring, inorganic substances with a definite chemical formula and crystal structure. Every rock is made up of one or more minerals, and the properties of these minerals—such as hardness, cleavage, and solubility—govern the rock's susceptibility to weathering.

For instance, a mineral like quartz is very durable and resistant to weathering, while feldspar is more prone to alteration and reacting with water through hydrolysis. As a result, granites, which contain both quartz and feldspar, will weather differently on their quartz and feldspar surfaces, illustrating the importance of mineral composition in weathering processes.

Different minerals react distinctly to environmental conditions. Calcite readily reacts with weak acids causing limestone, composed primarily of calcite, to chemically weather significantly. On the other hand, minerals with high silicate content withstand chemical weathering but can be susceptible to physical disintegration, showcasing the complexity and interplay between mineral composition and weathering processes.