Povondraite
Povondraite is a rare silicate mineral from the tourmaline group with formula: NaFe3(Fe4,Mg2)(BO3)3Si6O18(OH)3O. It is a dark brown to black nearly opaque mineral with a resinous to splendent luster. It crystallizes in the trigonal crystal system as equant, distorted prisms with trigonal pyramid terminations.