Minerals described in 1991

Abenakiite-(Ce) is a mineral of sodium, cerium, neodymium, lanthanum, praseodymium, thorium, samarium, oxygen, sulfur, carbon, phosphorus, and silicon with a chemical formula Na26Ce6(SiO3)6(PO4)6(CO3)6(S4+O2)O. The silicate groups may be given as the cyclic Si6O18 grouping. The mineral is named after the Abenaki, an Algonquian Indian tribe of New England. Its Mohs scale rating is 4 to 5.

Abswurmbachite is a copper manganese silicate mineral ((Cu,Mn2+)Mn3+6O8SiO4). It was first described in 1991 and named after Irmgard Abs-Wurmbach (born 1938), a German mineralogist. It crystallizes in the tetragonal system. Its Mohs scale rating is 6.5 and a specific gravity of 4.96. It has a metallic luster and its color is jet black, with light brown streaks.