This is a really amazing blue/green obsidian carved anatomical heart, with an acrylic stand. Obsidian is volcanic glass with varying inclusions that give it its different colors -- so yes, technically this is glass, but people still treat it as a crystal.
The skull is about 4" long and weighs 15 oz. I've never seen anything like these--these were a lucky find! We had two but the other one is gone.