Growing up in Hawai'i, I've spent a lot of time wandering around on lava flows both ancient and recent. Most of our lava is basaltic, which means, basically, it looks like what you expect lava to look like.
At the Newberry volcano, however, some of the flows are rhylotic, which (the geologists are going to come in and correct me here) partly means that they are 75% silica, vs. the ~50% silica of basaltic flows.
I found it remarkably hard to get a good picture there, so clearly More Time Is Required at the Big Obsidian Flow. This one gets pretty close to communicating how it felt.
This second photo represents a classic failure: a mediocre photo of a beautiful subject. The subject was my favorite of all of the structures I saw, but I wasn't able to make a photo that really expressed what I wanted it to.