This study characterizes the geochemical and mineralogical properties of volcanic soils in Central Java, Indonesia, focusing on samples from Yogyakarta, Klaten, and Wonogiri. The research incorporates analyses of major and trace elements, alongside mineralogical assessments using X-ray diffraction (XRD) and scanning electron microscopy (SEM). Results reveal that SiO₂, Al₂O₃, and Fe₂O₃ are dominant major oxides, reflecting derivation from volcanic parent materials and extensive weathering. Trace element analysis indicates that phosphorus and vanadium are significantly associated with iron oxides, while sulfur shows high mobility, implying ongoing leaching processes. XRD and SEM analyses identify halloysite, anorthite, and quartz as key mineral phases influencing soil structure, plasticity, and geotechnical behavior. High Loss on Ignition (LOI) values suggest the presence of secondary minerals and intense hydration. These findings underscore the need to integrate geochemical and mineralogical data into geotechnical evaluations, especially in volcanic regions with high urban development pressure.