Studtite : [(UO2)(O2)(H2O)2].2H2O

Source: Science (2012)

Why?

Studtite, or uranyl peroxyde, is a well-known compound in the nuclear fuel cycle used for decades. It's also a mineral, to date the only one involving uranium and peroxide. It's structure was only elucidate in 2003!—Blanchard Florent