Most of the glass we are familiar with is in the windows that let us look out of, and it's clear. However, there are many other variations of class such as slag from stained glass foundaries which can be vibrant and multi-colored 'rocks' that are man-made. Each year at the Quartzsite Desert Gardens show the Aussies always surprise with some other type of glass, usually out of China. Millefioric (thousand flowers), fiber optic, and opalite are among my purchases. I also have Goldstone in a category of it's own, but that is also a type of synthetic glass.
As I've said before, I'll try to cab anything that resembles a rock. Consequently, I've made many cabs from this interesting glass. It's hard and polishes to a high shine.