Vitroclastic texture

Ever since the discovery of analcime in tuffaceous rocks, most workers have assumed that the analcime formed directly from vitric material. The presence of vitroclastic texture and pyrogenic crystals in some anal-cimic tuffs seemed sufficient evidence however, these criteria do not necessarily prove that the glass altered directly to analcime. Hay (48) and Sheppard and Gude (123) concluded from a study of tuffs in saline-lake deposits that analcime commonly formed from alkalic, silicic zeolite precursors. Formation of analcime from clinoptilolite and phillipsite was documented in tuffs of the Miocene Barstow Formation. Relict fresh... 

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