English: Welded tuff from western USA. (Public display, Geology Department, Wittenberg University, Springfield, Ohio, USA). The banded to layered appearance of this sample is from the presence of many elongated, dark colored pieces. This is called "eutaxitic texture". It forms as pumice and/or glass-rich volcanic rock fragments become flattened. Volcanic tuffs are solidified volcanic ash deposits - they form by explosive volcanic eruptions. Some ash beds remained so hot after initial deposition that the heat was sufficient to self-solidify the beds. Such deposits are called welded tuffs. Some welded tuffs have glassy cores, where the ash was heated past the melting point after deposition (for example, the Late Miocene-aged Resting Spring Pass Tuff east of Shoshone, eastern California, USA).