Scanning electron micrograph of altered glassy rhyolite from around 140 m in drill hole Y-2. Yellowstone National Park, Wyoming. 1978.

Photo caption: 11/16/78. Y2 - 462.0. Mordenite. Figure caption: Scanning electron micrograph of altered glassy rhyolite from around 140 m in drill hole Y-2. Remnant perlitic texture is preserved by feathery clusters of intergrown short mordenite fibers generally oriented with their long axes perpendicular to former hydration cracks. X-ray diffraction also indicates the presence of illite. Scale bar is 30 microns. No index card. Published as Figure 4 in Zeolites in Yellowstone National Park. The Mineralogical Record; 12: 29-38.