Day #69 Deskcrop: Vitrophyre with Pumice Inclusion

Today’s deskcrop shares the textural designations hypocrystalline and porphyritic with yesterday’s, but I’ve chosen to identify today’s by another name: vitrophyre. I am much more certain of the locality where I collected this sample – it was from road grading material on Wyoming 89 near Lewis Falls in Yellowstone National Park – but it was not in place, so I’m uncertain whether it originated in the pyroclastic Lava Creek Tuff (in which case the obsidian would represent remelting of rhyolitic ash at the base of the pyroclastic deposits produced by the most recent caldera forming eruption at Yellowstone), or if it comes from the post-caldera obsidian/rhyolite domes that occur just upstream from this locality. In either case, its composition is more likely rhyolite than dacite, despite its similar texture and appearance compared to yesterday’s deskcrop.

Vitrophyre with Pumice Inclusion

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