Expansive soil contains montmorillonite clay mineral; which has tendency to swell by imbibing water in monsoon season and shrink or become harder by leaving cracks in drier seasons. Excessive drying and wetting of soil progressively deteriorates structures over the years and cause severe damage. Some research has been performed on identification of expansive soil and determination of its expansiveness and shrinkage–swelling potential based on its index properties at various wetting–drying conditions. Few researchers worked on the chemical stabilization of expansive soil to improve its mechanical behavior. However, the relationship of mineralogical properties of expansive soil with its shear strength and compressibility parameters is still unexplored; and these parameters are required in bearing capacity and settlement calculations for soil strata. The current research is focused on relationship of mineralogical properties (CEC, SSA, montmorillonite content) of expansive soil with its mechanical behavior including compressibility, shear strength, swelling potential and index parameters. This experimental research has been performed on expansive soil (black cotton soil) covering major part of Bhavnagar, located along the coast line of Gulf of Khambhat in Gujarat (India), which has serious construction issues due to its severe shrinkage–swelling behavior.