Extremely rare mineral (IMA 2011-017) in well formed acicular metallic crystals from the only known locality for the mineral worldwide that is, of course, the type locality: Herminia Mine, Julcani, Huancavelica Department, Peru. — Photo: David Hospital · CC BY-SA 4.0
Terrywallaceite
Terrywallaceite is an IMA-recognized mineral species in the sulfosalt class, with the chemical formula AgPb(Sb,Bi)₃S₆.
It crystallizes in the monoclinic crystal system (space group P2_1/c). It is a member of the Lillianite structural group.
Key properties: Mohs hardness 4; specific gravity 6.005; Black streak; Metallic luster.
IMA symbol Twl, IMA status: approved, named in 2011.
Found in hydrothermal veins that contain sulfosalt mineralization.
It is found associated with Tetrahedrite, gustavite, barite, pyrite.
The mineral was named to honor Terry C. Wallace Jr., former professor of geosciences and mineral museum curator at the University of Arizona, Tucson, USA. Since 2003.