Crystal caves

Now that the sulfur cube was added, should add a new crystal cave (like the one proposed in the caves and cliffs that turned in the amethist geode), this biome would be like a larger amethist geode with a higher concentration of diamonds, redstone and emeralds (also add the quartz crystal for this biome). And to balance it, this would be the newest rarest biome, generatind only under y = -20