Soil having a nature of volume change due to moisture content is called expansive problematic soil (EPS). The present investigation performs the mineralogical analysis for copper slag (CS) treated EPS without and with lime using X-ray diffraction (XRD) test results. For this purpose, the soil specimen was collected from Talab, Nainwa, Bundi, Rajasthan. The CS was added to soil specimens from 0–30% at 5% variations, and a significant improvement in maximum dry density, California bearing ratio, and unconfined compressive strength of EPS was obtained by adding 25% CS. Moreover, the 25%CS mixed specimen (CSS5) was cured for 7, 14, and 28 days, and found that the UCS of the CSS5 specimen was increased by 109.28% (wrt UCS of soil) at 28 days of curing because of Hedenbergite (H), Clinopyroxene Aluminous (CA), and Calcium Copper Aluminum (CCA) minerals. It has also been observed that no pozzolanic minerals were formed. Therefore, 0.5% free lime was added to the CSS5 specimen and cured for 7, 14, and 28 days. Interestingly, the UCS of CSS5 was increased by 144.8% (from soil UCS), 61.4% (from CSS5, no curing), and 17.0% (from CSS5 at 28 days curing, no lime). The pozzolanic minerals, such as Daphnite, Gismondine, Wollastonite, Tobermorite, Parawollastonite, and Sodium Aluminum Silicate Hydrate, were formed at 28 days of curing by adding 0.5% free lime.