Excellent, rather sharp crystal cluster of Moschellandsbergite from Landsberg in Germany. Usually a combination of Mercury and Silver that is amorphous, there was ONE FIND of this incredible material back in the 1800s. (Maybe it is apocryphal, but I heard that they had been out of the ground and not recognized as a new species for many decades.) Sharp crystals this size are quite uncommon. Previously in the collection of the Freiberg Academy. Per MINDAT: https://www.mindat.org/loc-1834.html, as follows an excerpt: An ancient mercury mining district. Moschellandsberg is world famous for being the type locality and providing by far the best crystals of the silver mercury amalgam moschellandsbergite. But also fine calomel crystals, native mercury, cinnabar and many rare mercury minerals make Moschellandsberg very interesting for the collector. Documented mining activities started around 1440 with heydays in the 16th, 18th and 19th centuries. Last activities started in 1934 but due to the poor mercury content of the remaining ores all mining work finally stopped in 1942. A superb, classic, rare and historic thumbnail specimen of something very hard to find for sale today!