Q. The black cotton soil of India has been formed due to the weathering of

Explanation : 

Black Cotton Soil and Its Formation

Black cotton soil, also known as Regur soil, is a type of vertisol found in India. This soil is particularly prevalent in the Deccan Plateau, which covers parts of Maharashtra, Madhya Pradesh, Gujarat, Andhra Pradesh, and Tamil Nadu. The black color of the soil is due to the presence of various minerals, including iron, magnesium, and aluminum silicates, which are derived from the weathering of volcanic rocks.

The correct answer to the formation of black cotton soil is “fissure volcanic rock.” This refers to the basaltic rock that originates from volcanic activity, particularly through fissure eruptions, where lava flows out of long cracks in the earth’s crust. Over time, these basaltic rocks weather under the influence of water, temperature changes, and biological activity, breaking down into smaller particles.

Weathering Process and Soil Characteristics

Weathering of these fissure volcanic rocks leads to the formation of fine-grained, clay-rich soil that has the capacity to retain moisture. The high clay content causes the soil to swell when wet and shrink upon drying, which can lead to deep cracks during dry seasons. This characteristic makes the soil suitable for growing cotton, hence the name “black cotton soil.” The soil is also rich in nutrients, making it fertile and good for agriculture, although its high clay content can pose challenges for building foundations due to its expansive nature.

Parent Materials of Black Cotton Soil

The other options listed—brown forest soil, granite and schist, and shale and limestone—are not the primary parent materials for the formation of black cotton soil in India. Brown forest soil is typically associated with forested areas and is not the result of volcanic rock weathering. Granite and schist are metamorphic and igneous rocks, respectively, and while they can contribute to soil formation through weathering, they are not the primary sources of black cotton soil. Shale and limestone are sedimentary rocks that also do not typically weather into black cotton soil.