Mineral Weathering

Weathering is the breakdown of rocks, soils and minerals (as well as wood and artificial materials) through contact with water, atmospheric gases, sunlight, and biological organisms. It involves physical disintegration as well as chemical dissolution, processes which go hand in hand in soil development.

Mineral weathering is a process characterized by chemical and physical breakdown of geologic materials, accompanied by the generation of dissolved solutes plus relatively stable new mineral phases. Weathering is important as:

1. a source of nutrients such as calcium, magnesium, potassium, sodium, iron, silica, and a variety of trace metals;
2. a source of acid neutralizing capacity or alkalinity;
3. a source of phosphorus and sulfur in certain types of geologic formations; and
4. a vital process contributing to formation of clay colloids or secondary minerals.

In watershed ecosystems, mineral weathering represents a crucial process of replenishment that helps to offset cation losses resulting from leaching and forest harvesting, and it restores alkalinity consumed by acidic deposition and soil acidification processes.

Chemical weathering of rocks and minerals is the principal source of several macronutrients required by the biota: Ca, Mg, K, P, Fe, Mn, etc. Dissolution of these elements plays a key role in determining the chemical composition of soil, soil solutions and downstream ecosystems. In the long-term mineral weathering also influences global climate because weathering of silicate minerals consumes CO₂ through the generation of bicarbonate alkalinity in streamwater. Weathering of silicate minerals in terrestrial ecosystems is critical to the supply of dissolved silica in riverine and eventually coastal and marine ecosystems where it is assimilated by diatoms and helps drive aquatic productivity.