Clay mineralogy and swelling — which clay mineral group typically does not swell appreciably when wetted?

Introduction / Context:
Volume change characteristics of clays are governed by their crystal structure and interlayer bonding. Swelling clays can cause significant foundation and pavement distress, whereas non-swelling clays are comparatively more stable with moisture changes.

Given Data / Assumptions:

• Clay groups considered: kaolinite, mica/illite (sometimes miswritten as “mite”), vermiculite, montmorillonite (smectite).
• Swelling potential is judged qualitatively under typical groundwater chemistry.
• No special salt interlayer treatments are assumed.

Concept / Approach:

Kaolinite has a 1:1 layer structure with strong hydrogen bonding between layers, limiting interlayer water entry and swelling. Montmorillonite (smectite) has a 2:1 structure with weak interlayer bonding, allowing significant water uptake and large swelling. Vermiculite also exhibits swelling (though often less than montmorillonite). Mica/illite shows limited to moderate swelling due to potassium-bridged interlayers but more than kaolinite.

Step-by-Step Solution:

Verification / Alternative check:

Index tests such as free swell index and activity correlate swelling with mineralogy; kaolinite-rich soils show low activity and low swell.

Why Other Options Are Wrong:

Montmorillonite — highly swelling.

Vermiculite — swelling to moderate-high, depending on cations.

Illite/mica (“Mite”) — limited swelling but not as low as kaolinite.

Common Pitfalls:

Assuming all 2:1 clays swell equally; overlooking role of exchangeable cations and salinity on swelling magnitude.

Final Answer:

Kaolinite group