I just got back from a 4 day field trip to the Long Valley Caldera in eastern California, so I'm a little behind on posting. The field trip was great and I had a chance to see a lot of pumice, a lot of welded tuff (in the form of the Bishop Tuff, the large ignimbrite that erupted from the Long Valley Caldera ~760,000 years ago) and got to lead the part that looked at the Mono domes (too bad snow covered the Inyo Domes). Pictured above some puffed obsidian - the layers are obsidian and vesicle-rich obsidian - that were erupted, cooled, expanded and cracked (known as "breadcrusting"). This is part of Panum Crater, the youngest of the Mono domes that comes in at ~600-650 years old.
Cool! I always thought of obsidian as black glassy stuff. This doesn't look like that at all!
Yes, there's lots of neat obsidian in that part of the world - and obsidian can be red, too!