Pegmatite rock formations

Pegmatite would be a new type of rock similar to diorite or andesite, but it generates near rarer ores e.g. diamonds and gold, possibly even the new amethyst geodes. It would serve as an indicator to miners that there may be larger quantities of rare and valuable gems and materials nearby, much like in real life. Generation wise, it forms in sheets of rock near diamonds and other valuables. The texture would have crystalline formations in it, and the stone part would  be grayish pink in color.

 

This feature would build on the devs' plan to add strategy to mining. You could be strip mining along and come across some Pegmatite, and instead of just continuing straight on you might consider investigating and digging around to see what you may have come across.