This is a superb, extra-large specimen of very finely branching, exceptionally sharp PSILOMELANE DENDRITES on LIMESTONE from Solnhofen, Germany. The natural, intricately detailed patterns on this limestone were formed in the Jurassic period, about 160 million years ago. Mineral rich water with high concentration of iron and manganese migrated into microscopic cavities between the layers of limestone, creating these stunning patterns, that have been mistaken for fossil ferns. Although they look like they were painted on the rock (and have been called picture rocks), this is a completely natural formation. We purchased this specimen from a German dealer who was set up at the Tucson Gem, Rock & Mineral Show. After looking over all of his material, we high graded the finest examples - and this was one of the prize finds of that day.