Montebrasite (twin)

Item Description

Please note that this specimen is not Amblygonite, which was a typical labelling mistake that took place with this material for many years, but it is in fact Montebrasite. After properly analyzing the material, it turns out that true Amblygonite is actually quite rare. The species are isostructural and are both lithium aluminum phosphates, but the difference is that Montebrasite has a hydroxide ion in its chemical formula, while Amblygonite has a fluoride ion. In terms of charge and size, the fluoride ion resembles the hydroxide ion, so it's easy to see why so many Montebrasites were labeled as Amblygonites back in the day. As a matter of fact, Amblygonite was mistaken for Scapolite many years ago, which is actually how Amblygonite got its name. Amblygonite was named from the Greek word "amblus" for blunt, and "gonia" for angle, because of the obtuse angle between the cleavages, which distinguished it from Scapolite. With that said, this is a beautiful "fishtail"-twin of Montebrasite with a very light golden-green hue, and decent translucency from Brazil. The piece is in very good shape, and the edges that might appear "chipped" are actually fully crystallized. From the collection of William ("Bill") (1927-2006) and Anne (1928-2021) Cook of Cleveland, Ohio (#10422). This husband and wife duo were actively involved in the mineral world for many decades. Bill was a PhD geologist, and Anne was a mathematician, and they both were very serious mineral collectors. Bill served for many years as adjunct curator of mineralogy at the Cleveland Museum of Natural History, and Anne was inducted into the Micromounters' Hall of Fame on October 12, 2019. Both Bill and Anne, at various times, served as president both of the Mineralogical Society of Cleveland and of the Micromineral Society of the Cleveland Museum of Natural History, and Anne was inducted into the mi The rare barium lithium beryllium phosphate Wilancookite was named in their honor in 2015.