Question

The dominant clay mineral present in Inceptisol is

• A. Montmorrilonite
• B. Illite
• C. Kaolinite
• D. Chlorite

Hint:

Think about the parent rock of Himalayan alluvium and how little it has weathered.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Inceptisols are soils that show only weak to moderate profile development. In India this order covers large parts of the Indo-Gangetic plains, formed from young alluvium washed down from the Himalayas.

Step 2: Key Formula or Approach:
The clay mineral that forms in a soil depends mostly on the parent rock and how much weathering the soil has gone through. Heavily weathered soils develop kaolinite or iron and aluminium oxides, basalt derived soils under poor drainage develop montmorillonite, and young soils formed from mica rich rock keep the clay mineral inherited from that rock.

Step 3: Detailed Explanation:
The Himalayan alluvium that built the Inceptisols of north India came from mica bearing rocks such as schist and gneiss. Since these Inceptisols are young and have not weathered much, they largely keep the mineral inherited from mica, which breaks down first into illite.
Montmorillonite forms mainly in Vertisols, the black cotton soils that developed from basalt under poor drainage, so option 1 does not fit Inceptisols.
Kaolinite is a simple clay mineral that needs long, intense weathering under high rainfall to form, seen in old, heavily weathered Alfisols and Ultisols, not in young Inceptisols.
Chlorite shows up in small amounts in many soils but it is never reported as the dominant clay mineral of Inceptisols.

Step 4: Final Answer:
The dominant clay mineral in Inceptisol is illite, so option 2 is correct.