It is basically a very thin, fine piece of glass. They are very pretty, and, unfortunately, my photography wasn't to great at the time, but it just gives you a better reason to go visit the Big Island. This looks a lot like the cinder you can buy at the store. Well you can, and many people actually have it at home. Cinder is the most common type of pyroclastic, found all over the world.
Some hardware stores sell it.
It lands solidly, and has many wholes and pockets in it. Sort of like a less hole-y, more solid form of reticulite. This spatter rampart holds very good examples of spatter, if you look closely. Spatter is exactly how it sounds, when the lava splats onto the ground still in it's liquid form. Sort of like when you drop mashed potatoes on the ground, it makes a splat.