This data release provides semiquantitative mineralogy results from X-ray diffraction (XRD) analyses of mineral scales from The Geysers vapor-dominated geothermal field in California. The mineral species and their abundances are reported in weight percent and values have been normalized to total 100 percent for each sample. The X-ray diffraction results show that the mineral samples from the wellheads are primarily composed of ammonium (NH4+) sulfate minerals and sassolite B(OH)3, whereas sulfide minerals such as cinnabar and pyrite are the most abundant minerals observed in the power plants. Mineral scales vary along the steam flow path, from the wellhead to power plants. Relatively abundant iron oxide and iron hydroxide minerals in some mineral scales indicate significant contamination of the scales by rust from steel pipes that transport the geothermal steam.