BY BOB RUSH
The swirly material shown is uncommon but is a definite indicator of it being present in some specimens.
Over the years I have become almost obsessed with working obsidian. It is rather abundant and the varieties that are possible are numerous. Most of the collecting sites are still producing examples of the classic colors and patterns in reasonable sizes. The most important thing is knowing and understanding how to properly orient the material to expose the particular pattern or effect that you are looking for.