I have no clue what happened here, and neither do any of the experts on MSH whom I asked. It LOOKS as if gonnardite has coated some other mineral species (Haineault proposes calcite as an educated guess) that has now vanished and left behind a hollow cast which has been nearly filled in by bright lemony-yellow crystals of shortite. The shortite has unusual form, in that the crystals are extended and pointy rather than barrel-shaped. Overall the piece is just plain odd, and really attractive in that oddball way. To my knowledge, it is unique in its completeness. I saw a number of other fragments that were probably from similar growths but this was the only complete crystal Gilles had for sale at the Rochester show and he felt it was the best for form, as well.