A great thumbnail of this rare iron arsenic sulfide. This species is known from a number of localities world wide, but the only ones that I have ever seen for sale (including this one) are from old (pre-1950) finds in the Cerro de Pasco area. This is a particularly good thumbnail, The ball of gratonite is positioned nicely on its matrix, and I can see only one missing crystal in the whole cluster.
This is a beautiful thumbnail of one of the rarer South American sulfides.