Tarnowitzite is a rare lead-rich varietal of aragonite (it is also called plumboan aragonite), here represented in a large, rich, striking and actually rather PRETTY specimen from the classic Tsumeb locality. Tarnowitzite is actually a mixture of aragonite and cerussite. The crystals here are not only superbly formed, but EXTREMELY lustrous; they stretch completely across the matrix from side to side.