Quite unusual cluster - almost a floater, given the semi-termination on the underside - and the top is a bit 'greener' than it looks in the photo (image 2 seems to capture the hue better). It seems to be a sort of Cactus Druze overlay over Quartz and/or Calcite, but I have since learned that it's a Prehnite.
Photos don't do this piece justice - it's milky white but quite transclucent - glittery. Very superior piece.
Stunning, glittery display piece, looks kind of blue gray lavender - and it sits atop what appears to be both blue and purple Fluorite - excellent on a stand!