Rocks and Soils

Hydroponics is a subset of hydro-culture and is a method of growing plants using mineral nutrient solutions, in water, without soil.

Petrology is the study of the origin, composition and structure of rocks.

Haematite, also spelled as hematite, is the mineral form of iron(III) oxide (Fe₂O₃).

Laterites are soil types rich in iron and aluminium, formed in hot and wet tropical areas. Nearly all laterites are rusty-red because of iron oxides. They develop by intensive and long-lasting weathering of the underlying parent rock.

Soil texture is given after the soil formation and it is not a factor of formation of soil.

Slate is a metamorphic rock formed from the metamorphism of shale. It's characterized by its fine grain and foliation (layering), allowing it to split into thin sheets. Sandstone and limestone are both sedimentary rocks, not metamorphic.

Alluvial soil is formed by accumulated sediments transferred by the rivers and rapids, so it is amongst the most fertile soils. Alluvial soils are well suited to irrigation which helps in raising a number of crops like rice, jute, sugarcane, wheat, cotton, maize, oil seeds, fruits and vegeta­bles.

Marble is a metamorphic rock formed from the metamorphism of limestone, not a sedimentary rock. Limestone and sandstone are classic sedimentary rocks formed from compressed sediments. The question asks which is NOT sedimentary, making marble the correct answer.

Peat, bituminous, and lignite are all types of coal - sedimentary rocks formed from compressed plant matter. Graphite, however, is a mineral (a form of carbon) formed through metamorphic processes, not from the coal formation pathway. It has a completely different origin and crystal structure.

Red soil, black soil, and peaty soil are all associated with tropical or subtropical regions (red and black soils are typical of tropical India, peaty soils form in tropical wetlands). Brown soil, however, is typically associated with temperate regions (like brown forest soils in Europe and North America), not tropical climates.

Laterite soil is formed in hot, wet tropical areas through intensive leaching - heavy rainfall washes away soluble minerals like silica and lime, leaving behind insoluble iron and aluminum oxides. This gives laterite its characteristic red/orange color. Black soil (regur) is a volcanic soil rich in clay, not formed through leaching.

Soil formation occurs through weathering - the breakdown of rocks and minerals through physical (temperature changes, frost), chemical (dissolution, oxidation), and biological (plant roots, microorganisms) processes. Erosion moves soil but doesn't create it; deposition is the settling of eroded material; denudation is the overall process of wearing down landscapes.

Loess is a wind-deposited soil - it's composed of fine silt and dust particles carried by wind and deposited over large areas. Unlike alluvial (water-deposited) or glacial soils, loess forms from aeolian (wind) processes. This creates its characteristic homogeneous, loosely packed structure.

China has the world's largest and most extensive loess deposits, particularly the Loess Plateau covering ~640,000 km². These deposits were formed from windblown silt from the Gobi Desert. Central Europe, New Zealand, and Argentina have loess, but not on China's scale.

Limestone is a sedimentary rock composed largely of the minerals calcite and aragonite, which are different crystal forms of calcium carbonate (CaCO₃).