Petrified wood is one type of fossil.
The term fossil originated from the Latin word fossilis that means "dug up." Any organic remains preserved in part of the Earth's crust are fossils, though the most interest lies in fossils of extinct plants or animals. Fossils tend to occur in sedimentary rock, which is affected by the processes that change geography, like wind or water. Fossils are categorized as either body or trace fossils. Body fossils reveal the shape of an organism, while trace fossils give clues to their activities. Within those classifications, there are an additional five types of fossils.
Cast Fossils
Cast fossils occur when minerals replace the space left by an organism, such as a footprint. Cast fossils also occur when outlines of the organism's body structure, such as a mollusk's shell, become minerals. Replacement minerals can include pyrite, silica, iron and calcite.
Actual Remains
Actual remains fossils consist of the entire organism preserved as a fossil. The process occurs through unaltered preservation, when an organism is preserved in a substance like ice, tar or amber after dying in the substance. Amber is hardened tree sap.
Mold Fossils
Mold fossils are like a negative impression of the organism that became trapped in the sediment layer. Mold fossils leave a hollow impression in the rock they have formed inside. Common examples of mold fossils are feather or leaf imprints.
Fossil Fuels
Fossil fuels developed during the Carboniferous period, about 360 million to 276 million years ago. The planet was covered with swampland. Animals and plants died and degraded, settling into the sediment. Over time, they were compressed until only carbon remained. Oil, natural gas and petroleum are all fossil fuels.
Petrified Wood
Petrify means "turn to stone." According to Northern State University in South Dakota, the petrification process isn't fully understood. Scientists know the plant matter must have been trapped in an environment where it was deprived of oxygen to preserve the wood. Minerals replace the wood over time, literally turning it to stone. Quartz is the most prevalent mineral found in petrified wood. Chrome, copper and iron also can occur in trace amounts, all of which can cause variations of color.
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