Naturally occurring asbestos (NOA) refers to asbestos found as a natural component of rocks and soils. The purpose of this study was to determine effective methods for changing the characteristics of NOA. Unprocessed chrysotile-containing soils and rocks were treated using heat (700–1100°C for 1–3 hours) and combination (100–250°C, 0.3–1.0 M oxalic acid for 1–3 hours) methods. A polarized light microscope (PLM) and field emission scanning electron microscope (FE-SEM) with an energy-dispersion spectrometer (EDS) were used for the analysis of both untreated and treated samples. While PLM analyses revealed gradual change in optical properties in both heat and combination treatments, SEM/EDS analyses revealed morphological and chemical changes under conditions of combination treatment. The elemental composition of combination treated samples showed low levels of magnesium and high levels of silicon compared to untreated samples. The optimal treatment condition was 1 M oxalic acid at 250°C temperature for 1 hour. Combination treatment resulted in changes in NOA characteristics at lower temperatures than did heat treatment alone.