Fig. 13. Optical photomicrographs of textures of nonwelded tuffs. (A) Plane-polarized light image of undeformed tuff from the Horton Creek site. Pumice (P) at right contains elongate vesicles and numerous smaller pumice lapilli in a matrix of glass shards and ash. (B) Plane-polarized light image of open fractures (F) in a feldspar phenocryst that appear to be truncated at the pumice grain boundary at center of image. (C, D) Fragmentation of tuff samples from the Crucifix site. Fractured quartz grains (Q) lie next to relatively undeformed pumice (P) and a matrix of cataclastically deformed grains (C). (E) Cross-polarized light image of cataclastically deformed sample at the Crucifix site (BT-50). Birefringent material is calcite filling the fault. (F) Calcite-filled cataclasite in a fault zone from the Crucifix site. CC, calcite.