1) Manganese mineral 2) Trigonal mineral
Found on
https://www.crosswordclues.com/clue/povondraite
Povondraite is a rare silicate mineral from the tourmaline group with formula: NaFe3+3(Fe3+4,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. It occurs as rare fracture and cav...
Found on
http://en.wikipedia.org/wiki/Povondraite
No exact match found.
