so i have a size 400 purity 81% and cutting 100% and have used over 32 liquid starlight buckets to try and make it split but it still hasn't split.

Sounds like you need to check the config options for the pack you are playing, because while it may be possible RNG hates you that much, it is more likely that splitting is disabled in the pack you are playing. Check for the "canCrystalGrowthYieldDuplicates" setting.

Esp if you're playing FTB:Interactions.