Geo 365: March 27, Day 86: Fire on the Motel

I had been planning on moving on from the obsidian in the motel facade today, but I realized I had a pair of photos from different angles that illustrate the "fire" quite nicely. It's only barely visible at the above scale, but if you click to enlarge, you can see the play of light is visible in the left ellipse, but not in the right. As a viewer moves, or slowly turns a loose cobble in their hands, you can see reddish-orange-gold flickers skimming through the rock's interior. "Fire mahogany," however useless it is as a geologic term- we'd just lump it all as obsidian- is a truly apt name for this rock.

Photo pair cropped and joined, otherwise not processed. August 20, 2011. FlashEarth Location.

Followup: I forgot to mention this when I first wrote it up, but it's important and interesting enough to add it on: Note the conchoidal fracture, originating from the edge on the lower right. That shell-like pattern persists across the whole exposed surface. Looking carefully, you should be able to see little streaks, like meteorites, perpendicular and radial to the conchoidal fracture, and if you look at the full-size version, you can indeed see little white blebs at the head of each, at the end of the streak toward the impact spot at the lower right. Those white blebs are phenocrysts- sanidine would be an educated guess- that disrupted the shock/fracture front as it propagated. So if you look over the entire exposed rock, you can see that the whole surface was created by one impact and one fracture.