Manganese Dendrite Plaque

A dendrite is a superficial deposit of manganese oxide that has crystallized in a multi-branching tree-like pattern.  Often misidentified as fossils since the branching pattern resembles leaves, dendrites form as water rich in manganese and iron flows along tiny cracks between layers of limestone and other rock types.  Dendrites may also consist of iron oxides and other minerals, and can also form in quartz materials like agate and jasper. In Solnhofen, Germany, dendrites line fractures in 160 million year old marl, or calcareous mudstone, a sedimentary rock.