A doublet is a cab made up of two parts. The top is Spencer Opal. The bottom is a dark black rock. People use obsidian, black petrified wood, and other rocks to provide a backing. That, and Nathan's skill made the fire in the opal come alive.
The opal is found in a pay-to-dig mine near Spencer, Idaho. I think my dad got the better part of the deal because nobody could dig better than my dad. When he was there, it was an hourly charge and my dad hauled quite a bit of opal out of the mine. I'm not sure what their rules or prices are now but you can search for their web page.
