Which one of the following statements is not correct regarding clay minerals ?
- AThe typical range of shrinkage limit of Kaolinite is 8·5 – 15.Correct
- BThe typical range of shrinkage limit of Illite is 15 – 17.
- CThe typical range of liquid limit of Montmorillonite is 100 – 900.
- DThe typical range of plastic limit of Montmorillonite is 50 – 100.
Solution
Concept
Typical Atterberg limits of clay minerals
Step-by-step solution
1. Kaolinite: LL 30–110, PL 25–40, SL 25–29. 2. Illite: LL 60–120, PL 35–60, SL 15–17. 3. Montmorillonite: LL 100–900, PL 50–100, SL 8.5–15. 4. The range 8.5–15 belongs to montmorillonite, not kaolinite.
Explanation
Montmorillonite is the most expansive clay mineral and has the lowest shrinkage limit (8.5–15). Kaolinite is the least active clay and has a higher shrinkage limit (25–29).
Why the other options are wrong
Statements (b), (c) and (d) agree with the typical values.
Shortcut
SL: kaolinite 25–29 > illite 15–17 > montmorillonite 8.5–15.
Common mistake
Giving montmorillonite's range to kaolinite.
Correct answer: A) The typical range of shrinkage limit of Kaolinite is 8·5 – 15.