Coal veins spawn around diamonds

Since it's possible for coal to turn into diamonds in real life because they're made of the same element, it would be cool to find diamonds in the core of a coal vein. A lot of players tend to not mine an entire coal vein. But knowing that there could be diamonds around coal makes players want to mine out all the coal and encourages players to go caving more often. It's a subtle change but I feel like it can greatly enhance the caving experience.

(Note: diamonds are not changing, they are still spawning at the same y-levels with the same spawn rates. Some of them are just going to be encased in coal.)