Fumarolic activity affects surrounding rocks and pyroclastics. Carbonates, opal, and white covers of possibly aluminum sulfate and calcium sulfate have been formed. Gypsum formed from the sulfur of the volcano is found in the form of crystals in the upper valleys of Taftan. Sinter and hydrothermally altered rocks are found farther down. Minerals formed by alteration processes include alunite, calcite, cristobalite, illite, jarosite, kaolinite, pyrophyllite, quartz, smectite, sulfur and tridymite. Some epithermal mineralizations have been identified around Taftan. Other secondary factors at Taftan include lahars.