Fig. 12. Mosaic of backscattered scanning electron micrograph of nondeformed nonwelded tuff from the Horton Creek site. Large feldspar phenocrysts (F), vesiculated pumice lapilli (P), and quartz grains (Q) lie in a matrix of irregularly shaped glass shards and ash. Intragranular fractures in the quartz may be the result of rapid cooling from the caldera. Images acquired with 10 KV accelerating voltage.