X-ray powder diffractometry/Rietveld refinement was employed to estimate the purity of several chrysotile powders for calibrating standards. α-Corundum powder was mixed into each chrysotile sample as an internal standard. X-ray diffractometry was performed on these mixtures, and the mass fractions of amorphous and impurity phase content were calculated using Rietveld refinement. The chrysotile samples had 56.7 - 92.0% crystalline purity. X-ray diffraction intensities of chrysotile (002) from the samples showed good correlation with the crystalline purity data. In differential thermal analysis results, the exothermal peak intensities were found to be directly proportional to crystalline contents for crystalline purity lower than 80%. Any chrysotile sample can be used as a standard material for quantitative determination upon correction of the crystalline purity, which can be estimated using the proposed method.