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GATE 2018 CE (CE2) – Question 21

Geotechnical Engineering · Three-phase system, phase relationships, index properties and soil classification · 1 mark · Multiple choice

Which clay mineral has structural units held together by potassium bonds?

  1. Halloysite
  2. Illite
  3. Kaolinite
  4. Smectite

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Show answer and explanation

Correct answer: (B) Illite

Explanation

Illite has a 2:1 layer structure with potassium ions binding adjacent structural layers, limiting interlayer expansion. Therefore **illite, B** is the intended mineral. Smectite has more readily exchangeable interlayer cations and much greater swelling potential.