Montebrasite

Item Description

A fine quality, sharp, well-formed, gemmy, pale yellow color crystal of the rare phosphate Montebrasite from the famous Sapucaia Mine in Brazil. My favorite aspect of the piece is that it's actually crystallized(!) and not just an etched "lump" like the majority of the piece I've seen from this locality. There are not many localities in the world that produce fine crystals of Montebrasite this size, and Brazil is still the single most productive country in terms of the amount of Montebrasite discovered. Please note that this is not Amblygonite, which was a typical labelling mistake that took place with this material years ago. 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. A little over 200 years ago (in 1817), 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.
From the collection of Vasco Trancoso, a medical doctor and prominent mineral collector from near Lisbon, Portugal (https://www.mindat.org/user-11954.html). He assembled his mineral collection over the course of 60 years, and built a fine worldwide display collection that we recently purchased. This piece is pictured on mindat at https://www.mindat.org/photo-188065.html