This is a handsome and interesting piece! It is a plate of white celestine crystals with a darker core that shows through in center of the terminations. Some people say that these types of celestine crystals from this locality are partially altered to strontianite. I'm not sure. Interestingly, each celestine crystal has a couple of few small calcite crystals in the center of the termination.
As well the celestine is fluorescent, although not like in the photo. The crystals show as cramy white on the prisms while the terminations are a yellow colour. I could not seem to get hew fluorescent colours correct in the photo here. Excellent specimen from a classic mid-west locality.