Permineralization is a process of

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

ization of bones and tissues in which mineral deposits form internal casts of organisms. Carried by water, these minerals fill the spaces within organic tissue. Because of the nature of the casts, permineralization is particularly useful in studies of the internal structures of organisms, usually of plants.

Process

Permineralization, a type of fossilization, involves deposits of minerals within the cells of organisms. Water from the ground, lakes, or oceans seeps into the pores of organic tissue and forms a crystal cast with deposited minerals. Crystals begin to form in the porous cell walls. This process continues on the inner surface of the walls until the central cavity of the cell, the lumen, is completely filled. The cell walls themselves remain intact surrounding the crystals.

Silicification

silicification In geology, silicification is a petrification process in which silica-rich fluids seep into the voids of Earth materials, e.g., rocks, wood, bones, shells, and replace the original materials with silica (SiO2). Silica is a naturally existing and ...

, the

weathering Weathering is the deterioration of rocks, soils and minerals as well as wood and artificial materials through contact with water, atmospheric gases, and biological organisms. Weathering occurs ''in situ'' (on site, with little or no movement) ...

of rocks releases silicate minerals and the

silica Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is ...

makes its way into a body of still water. Eventually, the mineral-laden water permeates the pores and cells of some dead organism, where it becomes a gel. Over time, the gel will dehydrate, forming an

opal Opal is a hydrated amorphous form of silica (SiO2·''n''H2O); its water content may range from 3 to 21% by weight, but is usually between 6 and 10%. Due to its amorphous property, it is classified as a mineraloid, unlike crystalline form ...

ine crystal structure that is an internal cast of the organism. This accounts for the detail found in permineralization. Silicification reveals information about what type of environment the organism was likely to have lived in. Most

s that have been silicified are

bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typically a few micrometr ...

, algae, and other plant life. Silicification is the most common type of permineralization.

Carbonate mineralization

Carbonate mineralization involves the formation of coal balls. Coal balls are the fossilizations of many different plants and their tissues. They often occur in the presence of seawater or acidic peat. Coal balls are calcareous permineralizations of peat by

calcium Calcium is a chemical element with the symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar t ...

and

magnesium Magnesium is a chemical element with the symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 of the periodic ta ...

carbonates. Often spherical in shape and ranging from a few grams to several hundred kilograms in mass, coal balls are formed when water containing carbonate permeates the cells of an organism. This type of fossilization yields information about plant life in the Upper Carboniferous Period (325 to 280 million years ago).

Pyritization

This method involves the elements sulfur and

iron Iron () is a chemical element with Symbol (chemistry), symbol Fe (from la, Wikt:ferrum, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 element, group 8 of the periodic table. It is, Abundanc ...

. Organisms may become pyritized when they are in marine sediments saturated with iron sulfides. (

Pyrite The mineral pyrite (), or iron pyrite, also known as fool's gold, is an iron sulfide with the chemical formula Fe S2 (iron (II) disulfide). Pyrite is the most abundant sulfide mineral. Pyrite's metallic luster and pale brass-yellow hue giv ...

is iron sulfide.) As organic matter decays it releases sulfide which reacts with dissolved iron in the surrounding waters. Pyrite replaces carbonate shell material due to an undersaturation of carbonate in the surrounding waters. Some plants become pyritized when they are in a clay terrain, but to a lesser extent than in a marine environment. Some pyritized fossils include Precambrian microfossils, marine arthropods and plants. Raiswell, R. (1997). A geochemical framework for the application of stable sulfur isotopes to fossil pyritization. ''Journal of the Geological Society'' 154, 343-356.

Scientific implications

Permineralized fossils preserve original cell structure, which can help scientists study an organism at the cellular level. These are three-dimensional fossils, which create permanent molds of internal structures. The mineralization process itself helps prevent tissue compaction, which distorts the actual size of organs. A permineralized fossil will also reveal much about the environment an organism lived in and the substances found in it since it preserves soft body parts. This helps researchers investigate the plants, animals, and microbes of different time periods.

Examples of permineralization

* Most

dinosaur bones A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

are permineralized. *

Petrified wood Petrified wood, also known as petrified tree (from Ancient Greek meaning 'rock' or 'stone'; literally 'wood turned into stone'), is the name given to a special type of '' fossilized wood'', the fossilized remains of terrestrial vegetation. ' ...

: Permineralization is the first step in

petrification In geology, petrifaction or petrification () is the process by which organic material becomes a fossil through the replacement of the original material and the filling of the original pore spaces with minerals. Petrified wood typifies this proce ...

. In petrification, the cellulose cell walls are completely replaced by minerals. * Some examples of soft-bodied pyritization are Beecher's Trilobite Bed (

Ordovician The Ordovician ( ) is a geologic period and system, the second of six periods of the Paleozoic Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start of the Silurian Period Mya. T ...

) and the

Hunsrück Slate The Hunsrück () is a long, triangular, pronounced upland in Rhineland-Palatinate, Germany. It is bounded by the valleys of the Moselle-Saar (north-to-west), the Nahe (south), and the Rhine (east). It is continued by the Taunus mountains, past ...

( Devonian)

References

{{reflist Geological processes Fossilization Mineralogy concepts