These crystals are GLASSY and gemmy, in a way that only 1 in 10,000 feldspar specimens attains. It takes a powerful feldspar to overwhelm my prejudice against this common rock-forming species and love it on its own merit as a mineral specimen. I have loved this piece since I first saw it in a friend's collection in Brussels, many years ago. This is a wonderfully geometric specimen of stacked, glassy and gemmy, nearly colorless adularia crystals that are selectively coated by grayish-green chlorite (but not in an ugly way, or completely, as are so often the cases - in this rare instance, the coating works, for lack of a better way to put it). The crystals reach 4.4 cm in length. They are razor sharp and have the high luster of adularia. Ex. Wouter Van Tichelen collection along with his label (and further provenance on back). This is not "just a feldspar," but is rather one of the most mesmerizing Swiss specimens I have had in some time. Note that it is better in person, as it is hard to photograph for luster and transparency, both.