Question

Arrange the following in decreasing order of Basal Spacing:
(A). Kaolinite,
(B). Montmorillonite,
(C). Illite,
(D). Vermiculite

Choose the correct answer from the options given below:

• A. (A), (B), (D), (C)
• B. (A), (B), (C), (D)
• C. (B), (A), (D), (C)
• D. (B), (D), (C), (A)

Hint:

Expanding 2:1 clays (like Montmorillonite) always have larger basal spacing than non-expanding 2:1 (Illite) or 1:1 (Kaolinite) clays due to water molecules in their interlayer spaces.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Basal spacing (d-spacing) is the distance between repeating layers of a clay mineral, typically measured using X-ray diffraction (XRD).

Step 2: Detailed Explanation:
The basal spacing of these clay minerals under standard hydrated conditions is:
- (B) Montmorillonite: An expanding 2:1 clay mineral with a variable basal spacing that typically ranges from 1.4 nm to over 2.1 nm (14--21 \(\text{\AA}\)) depending on hydration and interlayer cations.
- (D) Vermiculite: A limited-expansion 2:1 clay mineral with a basal spacing of about 1.4--1.5 nm (14--15 \(\text{\AA}\)).
- (C) Illite: A non-expanding 2:1 clay mineral with a fixed basal spacing of approximately 1.0 nm (10 \(\text{\AA}\)).
- (A) Kaolinite: A 1:1 clay mineral with a fixed basal spacing of approximately 0.72 nm (7.2 \(\text{\AA}\)).
Arranging these in decreasing order yields: Montmorillonite (B) \(\gt\) Vermiculite (D) \(\gt\) Illite (C) \(\gt\) Kaolinite (A).

Step 3: Final Answer:
The correct decreasing sequence is (B), (D), (C), (A).