This is a major specimen of huge import! It is a rare example of a large euhedral crystal of this species, and the style of crystallization was found apparently just once and long ago (pre-1940). It was part of a piece in the BMNH that Mark much admired and one day he asked the curator if they might have a small sample for him of this material. To his surprise, this piece at some point was trimmed right off the major single piece at the BMNH,