Ok I am gonna take a shot at this and I am not very good at putting to words what is in my head so hopefully you can get the idea and someone can explain it better or tell me I totally missed the boat - I am very new to mica's but this is what I am thinkin' - Mica's do not dissolve, they are made to suspend in products which give them there sheen - so the results you are getting on the top of your soap could be a portion of mica that is not totally incorporated ( coated) with the soap. And as the soap is drying, it is leaving some of the mica sitting on outside of your soap thus the cracking effect. But in any case they STILL look great!