I'd just like to see what someone can do with a completely random subject. Think of the crystal as a generic prism shape with red inside. It doesn't necessarily have to be barb, but you must emphasize its relevance to the story.
As far as the double-sided coin, it can be used metaphorically, as in bipolar disorders or general two-faced people. Perhaps with the intention of taking said crystal.

In my dream last night, they were buried by sand and had influence over any who saw them. Anyone who came across these crystals would kill to get their hands on more- and those with power over them would manipulate others promising payment by way of crystal.
The double sided coin pops up when I thought I had a friend who was immune to its influence, but was actually just using my immunity to gather the crystals for herself.