Black manganese oxide dendrites created the “tree” in this petrified wood cab.
I’ve always been fascinated by dendrites, with their tree-like thin black lines that look as if a mineral suddenly took root at the base of the rock and grew. It’s the branching out, even though it is two dimensional, that looks like a tree. We see dendrites in all sorts of rocks, from sedimentary to metamorphic, agates, petrified wood, and jasper, to name a few. In my opinion, they are one of the oddities of the mineral world. They look so delicate and so artistically made yet are nothing more than the restricted growth of mineral crystals, usually a black manganese oxide.
What brought to mind the dendrites attractive designs was my recollec-tion of a nice specimen I saw at the August Rocky Mountain Federation Show that was held in Prescott, Arizona, in 2019. I talked about the specimen with the dealer, and during our conversation, he said the mineral was probably pyrolusite. I realized that his assessment was just a guess since collectors often assume the black manganese dendrite is pyrolusite. In all likelihood, it’s probably several common manganese oxides, because black dendrites can indeed be any one of several such manganese oxides of this very common metal element.