Weathering of Minerals: 3 Factors

This article throws light upon the three main factors affecting the weathering of minerals. The factors are: 1. Climatic Conditions 2. Physical Characteristics 3. Chemical and Structural Characteristics.

Factor # 1. Climatic Conditions:

The climatic conditions will tend to control the kind and rate of weathering. Under conditions of low rainfall or precipitation, there is predominant of physical weathering resulting decreasing in their sizes and thereby increases the surface area with little change in volume.

On the other hand, the increase in moisture content encourages both chemical and physical changes and thus facilitates the production of soluble and new mineral compounds.

In humid temperate regions, silicate clays are synthesized. Generally the rate of weathering especially chemical weathering is very fast in humid tropical regions. Under this condition, the more resistant products of chemical weathering like hydrous oxides of iron and aluminium, tend to accumulate.

Climate also mostly controls the dominant types of vegetation which in turn regulates the biochemical reaction in soils and mineral weathering.

Factor # 2. Physical Characteristics:

Various physical properties of minerals like size of the mineral, hardness and degree of cementation and the composition of rocks etc. are main parameters which influence weathering.

Composition of Rocks:

The phenomenon of breakdown or disintegration encourages due to differential composition of different minerals present in rocks. During the change of temperature, the amount of expansion and contraction varies and as a result due to presence of different minerals the differential stress develops and breaks the rocks into mineral components by forming cracks.

Size of the Mineral:

The fine sized feldspars will decompose more easily and rapidly than that of coarse sized feldspars exposing to percolating water. Besides this the more chemical reaction will take place in case of finer sized minerals. As for example, sand-sized quartz is extremely resistant to chemical weathering as compared to clay-sized quartz.

Hardness and Cementation:

Hardness and cementation influence weathering primarily by their effect on the rate of disintegration into finer particles which favours the chemical weathering. As for an example, a dense quartzite or sandstone cemented firmly with a slowly weathered mineral will resist physical weathering and leave a very small amount of total surface area for the chemical reaction.

On the other hand, porous rocks like volcanic ash or coarse sized limestone’s are very easily disintegrated into smaller sized particles facilitating the chemical reaction very rapidly because of large total surface area.

Factor # 3. Chemical and Structural Characteristics:

The ease of decomposition of a mineral depends upon its size, chemical and crystalline characteristics. As for example, gypsum (CaSO₄.2H₂O), which is sparingly soluble in water, is dissolved and removed in solution form in the presence of sufficient water either through irrigation or rainfall.

The dark coloured ferromagnesian minerals are more sensitive to chemical weathering than that of feldspars and quartz owing to their open structures resulting from the positively charged metallic ions of iron and magnesium balancing the negative charge of tetrahedra units.

The arrangement and packing of crystals may influence the rate of weathering. For instance less tightly packing olivine and biotite mica which are relatively easily weathered minerals as compared to relatively tight packing minerals zircon and muscovite.