If you use the WorldGenMinable(IBlockState, int, Predicate<IBlockState>) constructor, you can provide a Predicate<IBlockState> that matches the blocks you want your block to generate in.
If you use the WorldGenMinable(IBlockState int) constructor, the Predicate<IBlockState> will default to an instance of WorldGenMinable.StonePredicate; which matches the "natural" variants of Blocks.STONE (regular stone and the non-smooth variants of granite, diorite and andesite).
Please don't PM me to ask for help or to join your mod development team. Asking your question in a public thread preserves it for people who are having the same problem in the future. I'm not interested in developing mods with people.