Black soil in Madhya Pradesh is formed by which rock?
- (a)Sandstone
- (b)Limestone
- (c)Basalt
- (d)Gneiss
Correct — C, Basalt. Black soil (regur / black cotton soil) is a residual soil formed in situ by the prolonged weathering of basalt — the fissure-eruption lava rock of the Deccan Trap. Iron, magnesium and clay minerals (chiefly montmorillonite) released during this weathering give the soil its dark colour, high moisture retention, and characteristic self-ploughing (cracking) behaviour when dry. Madhya Pradesh's Malwa and Nimar plateaus, built on this basalt-capped Deccan Trap, are the state's principal black-soil tracts.
- (a)Sandstone — Sandstone, a sedimentary rock, typically weathers into sandy, often reddish or yellowish soils — not the clay-rich black soil.
- (b)Limestone — Limestone weathers into calcium-rich (calcareous) soils, distinct from basalt-derived black soil.
- (d)Gneiss — Gneiss, a metamorphic rock common across peninsular India's older shield areas, is associated with red and lateritic soils, not black soil.
Black soil (regur / black cotton soil) is a residual soil formed in situ by the prolonged chemical weathering of basalt — the fissure-eruption lava rock that makes up the Deccan Trap. Its clay-rich, moisture-retentive, self-ploughing nature (from a high proportion of montmorillonite clay minerals) makes it well suited to cotton and other rain-fed crops.
The trap is confusing black soil's origin with a sedimentary rock like limestone (which weathers into calcareous soils) or a metamorphic rock like gneiss (associated with red and lateritic soils elsewhere in peninsular India) — black soil's parent rock is specifically the igneous, volcanic basalt.
- Black soil (regur/black cotton soil) forms from in-situ weathering of basalt — the Deccan Trap lava rock.
- Rich in iron, magnesium and montmorillonite clay, giving it high moisture retention and a self-ploughing (cracking) character when dry.
- Sandstone, limestone and gneiss weather into different soil types (sandy, calcareous, and red/lateritic soils respectively) — not black soil.
- Madhya Pradesh's Malwa and Nimar plateaus, sitting on the basalt-capped Deccan Trap, are major black-soil tracts.
Black soil forms specifically from basalt — the volcanic rock of the Deccan Trap, not from sedimentary or metamorphic rocks.
- Attributing black soil to a sedimentary rock (limestone/sandstone) instead of the igneous basalt
- Confusing gneiss (metamorphic, red/lateritic soils) with the volcanic origin of black soil
MPPSC/UPSC repeatedly test the parent-rock-to-soil-type chain — basalt-to-black-soil is the most-asked pairing — lock each major Indian soil type to its parent rock.
The black cotton soil of India has been formed due to the weathering of
- (a) brown forest soil
- (b) fissure volcanic rock
- (c) granite and achist
- (d) shale and limestone
Answer(b) fissure volcanic rock
Same core concept, asked almost directly: India's black cotton soil (regur) is formed by the weathering of fissure volcanic rock — i.e. basalt, the Deccan Trap lava that is this question's correct answer too.
- practice — not a real PYQ
Black cotton soil (regur) is especially suited to which crop, after which it is popularly named?
- (a)Wheat
- (b)Cotton
- (c)Rice
- (d)Tea
Answer(b) Cotton — hence 'black cotton soil'; its clay-rich, moisture-retentive character suits rain-fed cotton cultivation.
- practice — not a real PYQ
The Deccan Trap, the source rock for India's black soil, was formed by which geological process?
- (a)Marine sedimentation
- (b)Extensive fissure-type basaltic lava eruptions
- (c)Wind-blown (aeolian) deposition
- (d)Metamorphism of limestone
Answer(b) Extensive fissure-type basaltic lava eruptions (late Cretaceous-early Eocene) — this cooled lava is basalt, whose weathering produces black soil.