Campyllite is a variety of Mimetite, and these lustrous, well-formed crystals are exceptional for this mineral. Their luster, color, and habit are well above what you normally find, even from this classic locality. Moreover, this piece has such unique aesthetics, with the ball of lustrous crystals atop a quartz crystal itself covered with micro-mimetite druse, that it is an excellent specimen - that just happens to be also a killer thumbnail.