Pseudofossils are inorganic objects, markings, or impressions that might be mistaken for fossils. Pseudofossils may be misleading, as some types of mineral deposits can mimic lifeforms by forming what appear to be highly detailed or organized structures. One common example is when manganese oxides crystallize with a characteristic treelike or dendritic pattern along a rock fracture. The formation of frost dendrites on a window is another common example of this crystal growth. Concretions are sometimes thought to be fossils, and occasionally one contains a fossil, but are generally not fossils themselves. Chert or flint nodules in limestone can often take forms that resemble fossils. Pyrite disks or spindles are sometimes mistaken for fossils of sand dollars or other forms (see marcasite). Cracks, bumps, gas bubbles, and such can be difficult to distinguish from true fossils. Specimens which cannot be attributed with certainty to either the fossils or the pseudofossils are treated as dubiofossils. Debates about whether specific forms are pseudo or true fossils can be lengthy and difficult. For example, Eozoon is a complex laminated form of interlayered calcite and serpentine found in Precambrian metamorphosed limestones (marbles). It was originally (1863) thought to be the remains of a giant fossil protozoan, the oldest fossil known. Similar structures were subsequently found in volcanic rocks at Mt. Vesuvius, where high-temperature physical and chemical processes were responsible for their formation.
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