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Fig. 14. Single fractures in nonwelded tuff. (A) Mosaic of plane-polarized light photomicrographs of a sample parallel to and 1 cm from the Chalk Cove fault. Fracture (f) that traverses the sample cuts dense ash and glass-shard matrix with quartz (Q) phenocryrsts, lithic fragments (L), and an ash matrix (M). Fabric density is due to compaction and deformation associated with the fault. (B) Mosaic of backscattered scanning electron micrograph of natural fracture from the Crucifix site. Fracture (f) lies along the phenocryst and lapilli boundaries. Irregular fracture boundary is produced by the interaction of the fracture and the primary pores. Note that the matrix pores are in general much smaller than the fracture aperture, and the pore spaces (black regions) are not well connected. Q, quartz; F, feldspar; P, pumice.
