Pseudoboleite on Boleite (rare classic material) (ex Kay Robertson Collection)

Item Description

The Amelia Mine in the Boleo District of Baja California Sur, Mexico is world-famous for producing the finest known crystals of species like Cumengeite and Boleite. Occasionally, the Boleite crystals from this locality will have an epitaxial overgrowth of thin "plate"-like blades of Pseudoboleite. The two species are closely related, the key difference is that Boleite contains some silver content, while Pseudoboleite does not, but many people will often look at a Boleite crystal and not even realize that there is another mineral present. If you look closely on each face of this "floater" cubic crystal, you will see a very thin "protrusion" / overgrowth layer of Pseudoboleite, which essentially has the same dark cobalt or prussian blue color as the underlying Boleite, so it's difficult to realize that there are two species present. The next time you see a Boleite cube, look closely for these tiny overgrowths, as it almost is certainly the presence of epitaxial Pseudoboleite. This specimen is complete all around with no damage, and is a great example of this world-class, beloved material from what is essentially the type locality for both species. Ex Kay Robertson Collection (#7705). Kay was a prominent California collector, who specialized in European classics. She nearly lived 100 years from April 1920 - March 2020. See the article in the March-April, 2007 Mineralogical Record ( https://www.mineralogicalrecord.com/pdfs/Kay%20Robertson%20Collection.pdf ), and the 50+ page article in the German Magazine "Mineralien Welt" November-December 2017.