Figure F28. Photomicrograph of Sample 183-1137A-44R-4, 44-46 cm, from near the base of the crystal-vitric tuff in basement Unit 9 showing well-preserved cuspate and tricuspate glass shards. Such shards form during pyroclastic disruption of vesiculating magma. There is no evidence of welding in this interval. Note the embayed margins of sanidine crystals (see "Igneous Petrology"). Field of view = 1.40 mm (plane-polarized light).