Wikipedia
Plavnoite
Plavnoite is a very rare complex uranium sulfate mineral with the formula KMn[(UO)O(SO)]•3.5HO. Typically for the secondary uranium mineral, plavnoite contains uranyl groups. It was discovered in the Plavno mine in Jáchymov, Czech Republic. The Jáchymov site is known as a type locality for many rare and unique minerals.