Arrange the minerals in the order of decreasing weathering index:

(A) Kaolinite

(B) Montmorillonite

(C) Vermiculite

(D) Mica

Choose the correct answer from the options given below:

Correct option is A

Explanation of the Correct Option (a): (A), (B), (C), (D)
· Weathering index indicates the degree of weathering and stability of clay minerals.
· Decreasing order means from most weathered to least weathered.
Correct sequence:
· Kaolinite (A)
· End product of intense chemical weathering
· Highly stable mineral
· Forms under humid tropical conditions
· Hence, highest weathering index
· Montmorillonite (B)
· Moderately weathered mineral
· Expanding clay
· Less stable than kaolinite
· Vermiculite (C)
· Intermediate weathering product
· Often formed from mica
· Moderate stability
· Mica (D)
· Primary mineral or least weathered secondary mineral
· Source mineral for vermiculite and smectite
· Lowest weathering index
· Therefore, the correct decreasing order is: Kaolinite → Montmorillonite → Vermiculite → Mica
Explanation of Other Options
Option (b): (B), (C), (D), (A)
· Incorrect because:
· Kaolinite (most weathered) is wrongly placed last.
Option (c): (C), (D), (A), (B)
· Incorrect because:
· Order of stability and weathering is incorrect.
Option (d): (D), (A), (B), (C)
· Incorrect because:
· Mica (least weathered) cannot be placed first.
Key Points Related to the Question
· Kaolinite → Most weathered, most stable
· Montmorillonite → Moderately weathered
· Vermiculite → Transitional weathering product
· Mica → Least weathered, parent mineral