How do I Make a Custom Block Have a 50/50 Chance of Dropping 1 of 2 Certain Blocks?

I am making a block called "prinite" and I want to make it so it drops the purple prinite or the yellow prinite.
I want it to be a 50/50 chance. I've already messed with loot tables, but whenever I mine the block it either drops nothing, the yellow one, or the purple one, or both. How do I make it so it only drops one of the following? I also want to make it so you can pick up the base block with the silk touch enchantment.