Tsaregorodtsevite is a very rare and very strange aluminosilicate mineral that contains the tetramethylammonium ion. This sodalite group mineral is found at ONE locality, worldwide. I recall when the Fersman Museum started selling their extras in 1991, this was one of the most coveted of all rare species that came out the doors from their various expeditions. I got some directly at the time from curator Dmitriy Belakovskiy, who has himself been to this remote location on at least one expedition. I assume this specimen came form the same source, the only source so far as I know. I have owned several over the years, and I can say this is a SUPER and RICH specimen. It has lustrous and gemmy, pseudocubic crystals to 5 mm on chlorite mica schist.