If you can explain this incredible Quartz cast, more power to you, because I sure haven't been able to get a cohesive explanation for these rare, old polyhedral quartz forms from anybody over the years. They turn up rarely in Brazil, and so far as I know most people think they formed as a cast filling in some kind of latticework crystal deposit but nobody is sure. The exposed opening to the cavity is 3 cm, and the cavity extends virtually all the way into the specimen. The aesthetics and uniqueness are out of this world. Such complete examples, not broken or sawed down the middle already, are seldom found today on the market.