Figure F3. Digital photomicrograph (crossed nicols) of a subrounded acidic volcanic clast with feldspar phenocrysts set in a siliceous matrix; feldspar is sericitized and the rock includes secondary calcite. Surrounding grains are feldspar, quartz, and additional basaltic fragments. The matrix is micritic (interval 180-1116A-1R-1, 58-60 cm).