I see what you mean it does seem to have faces like a crystal. Although there are quartz crystals (druzy) associated with this I can't think of any other type of crystal besides maybe calcite that would be associated in this type of rock. It is curious though because it reminds me of staurolite. I don't know fossils very well, so there may be a type of fossil that has flat surfaces like that.

Not a fossil, but what about a pseudomorph of a crystal? Or (this might be stretching it a bit) an encased crystal that has since dissolved and has since been filled in with something else? *shrugs*

Yes, there is a lot going on in that whole piece, besides for the crystal looking thing. It does resemble a Staurolite crystal. I'm thinking a long the same lines as dave, that the original form has been replaced, or partially replaced, by ........? The original may have been a plant or something organic that decomposed and left a void that was later filled? Or maybe a large Calcite crystal that has been replaced?
It doesn't fluoresce. It doesn't look like pure chert, either? If it was a void from the beginning you would think it would be filled with the chert? It would be interesting to identify the composite matrix. What is the hardness of the matrix?
I wonder if any of the other strange shapes on the piece are related to the "crystal"?
Well done, Rob. Good question!
I'm going to sleep on it.