Dendrites are actually superficial chemical stains that grew over rock or mineral surfaces. Dendrites include a variety of manganese-oxide minerals, which form when supersaturated solutions of hydrous iron-manganese oxides penetrate a surface and precipitate on it. They are commonly found on bedding planes of siltstone, shale, or limestone. They can also occur in rock fractures and on the sides of crystals of quartz, etc. Dendrites are paper thin and branching. In many cases, they do resemble fossil plants, but they are not fossils.
A slab (15 cm tall and 21 cm wide) of dendrites on a bedding plane of siltstone.
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