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geology Geology () is a branch of natural science concerned with Earth and other astronomical objects, the features or rocks of which it is composed, and the processes by which they change over time. Modern geology significantly overlaps all other Ear ...
, petrifaction or petrification () is the process by which
organic material Organic matter, organic material, or natural organic matter refers to the large source of carbon-based compounds found within natural and engineered, terrestrial, and aquatic environments. It is matter composed of organic compounds that have c ...
becomes a
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 ...
through the replacement of the original material and the filling of the original pore spaces with
mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. ( ...
s.
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. ''P ...
typifies this process, but all organisms, from bacteria to vertebrates, can become petrified (although harder, more durable matter such as bone, beaks, and shells survive the process better than softer remains such as muscle tissue, feathers, or skin). Petrifaction takes place through a combination of two similar processes:
permineralization Permineralization is a process of fossilization 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, perminera ...
and replacement. These processes create replicas of the original specimen that are similar down to the microscopic level.


Processes


Permineralization

One of the processes involved in petrifaction is permineralization. The
fossils 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 in ...
created through this process tend to contain a large amount of the original material of the specimen. This process occurs when groundwater containing dissolved minerals (most commonly
quartz Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical form ...
,
calcite Calcite is a Carbonate minerals, carbonate mineral and the most stable Polymorphism (materials science), polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on ...
,
apatite Apatite is a group of phosphate minerals, usually hydroxyapatite, fluorapatite and chlorapatite, with high concentrations of OH−, F− and Cl− ions, respectively, in the crystal. The formula of the admixture of the three most common e ...
(calcium phosphate),
siderite Siderite is a mineral composed of iron(II) carbonate (FeCO3). It takes its name from the Greek word σίδηρος ''sideros,'' "iron". It is a valuable iron mineral, since it is 48% iron and contains no sulfur or phosphorus. Zinc, magnesium and ...
(iron carbonate), and
pyrite The mineral pyrite (), or iron pyrite, also known as fool's gold, is an iron sulfide with the chemical formula Iron, FeSulfur, S2 (iron (II) disulfide). Pyrite is the most abundant sulfide mineral. Pyrite's metallic Luster (mineralogy), lust ...
), fills pore spaces and cavities of specimens, particularly bone, shell or wood. The pores of the organisms' tissues are filled when these minerals precipitate out of the water. Two common types of permineralization are silicification and pyritization.


Silicification

Silicification is the process in which organic matter becomes saturated with
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 one ...
. A common source of silica is volcanic material. Studies have shown that in this process, most of the original organic matter is destroyed. Silicification most often occurs in two environments—either the specimen is buried in sediments of deltas and floodplains or organisms are buried in volcanic ash. Water must be present for silicification to occur because it reduces the amount of oxygen present and therefore reduces the deterioration of the organism by fungi, maintains organism shape, and allows for the transportation and deposition of silica. The process begins when a specimen is permeated with an aqueous silica solution. The cell walls of the specimen are progressively dissolved and silica is deposited into the empty spaces. In wood samples, as the process proceeds, cellulose and lignin, two components of wood, are degraded and replaced with silica. The specimen is transformed to stone (a process called lithification) as water is lost. For silicification to occur, the geothermic conditions must include a neutral to slightly acidic pH and a temperature and pressure similar to shallow-depth sedimentary environments. Under ideal natural conditions, silicification can occur at rates approaching those seen in artificial petrification.


Pyritization

Pyritization is a process similar to silicification, but instead involves the deposition of iron and sulfur in the pores and cavities of an organism. Pyritization can result in both solid fossils as well as preserved soft tissues. In marine environments, pyritization occurs when organisms are buried in sediments containing a high concentration of iron sulfides. Organisms release sulfide, which reacts with dissolved iron in the surrounding water, when they decay. This reaction between iron and sulfides forms
pyrite The mineral pyrite (), or iron pyrite, also known as fool's gold, is an iron sulfide with the chemical formula Iron, FeSulfur, S2 (iron (II) disulfide). Pyrite is the most abundant sulfide mineral. Pyrite's metallic Luster (mineralogy), lust ...
(FeS2). Carbonate shell material of the organism is then replaced with pyrite due to a higher concentration of pyrite and a lower concentration of carbonate in the surrounding water. Pyritization occurs to a lesser extent in plants in clay environments.


Replacement

Replacement, the second process involved in petrifaction, occurs when water containing dissolved minerals dissolves the original solid material of an organism, which is then replaced by minerals. This can take place extremely slowly, replicating the microscopic structure of the organism. The slower the rate of the process, the better defined the microscopic structure will be. The minerals commonly involved in replacement are
calcite Calcite is a Carbonate minerals, carbonate mineral and the most stable Polymorphism (materials science), polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on ...
,
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 one ...
,
pyrite The mineral pyrite (), or iron pyrite, also known as fool's gold, is an iron sulfide with the chemical formula Iron, FeSulfur, S2 (iron (II) disulfide). Pyrite is the most abundant sulfide mineral. Pyrite's metallic Luster (mineralogy), lust ...
, and
hematite Hematite (), also spelled as haematite, is a common iron oxide compound with the formula, Fe2O3 and is widely found in rocks and soils. Hematite crystals belong to the rhombohedral lattice system which is designated the alpha polymorph of . ...
. Biotic remains preserved by replacement alone (as opposed to in combination with
permineralization Permineralization is a process of fossilization 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, perminera ...
) are rarely found, but these fossils present significance to paleontology because they tend to be more detailed.


Uses

Not only are the fossils produced through the process of petrifaction used for paleontological study, but they have also been used as both decorative and informative pieces. Petrified wood is used in several ways. Slabs of petrified wood can be crafted into tabletops, or the slabs themselves are sometimes displayed in a decorative fashion. Also, larger pieces of the wood have been carved into sinks and basins. Other large pieces can also be crafted into chairs and stools. Petrified wood and other petrified organisms have also been used in jewelry, sculpture, clock-making, ashtrays and fruit bowls, and landscape and garden decorations.


Architecture

Petrified wood has also been used in construction. The Petrified Wood Gas Station, located on Main St
Lamar, Colorado Lamar is the home rule municipality that is the county seat and the most populous municipality of Prowers County, Colorado, United States. The city population was 7,804 at the 2010 United States Census. The city was named after Confederate s ...
, was built in 1932 and consists of walls and floors constructed from pieces of petrified wood. The structure, built by W.G. Brown, has since been converted to office space and a used car dealership.
Glen Rose, Texas Glen Rose is a city in and the county seat of Somervell County, Texas, United States. As of the 2012 census estimate, the city population was 2,502. History 19th century The area was first settled in 1849 by Charles Barnard, who opened a tradin ...
provides even more examples of the use of fossilized wood in architecture. Beginning in the 1920s, the farmers of
Somervell County, Texas Somervell County ( ) is a county on the Edwards Plateau in the U.S. state of Texas. As of the 2020 census, its population was 9,205. Its county seat is Glen Rose. The county is named for Alexander Somervell, secretary of war for the Republic of ...
began uncovering petrified trees. Local craftsmen and masons then built over 65 structures from this petrified wood, 45 of which were still standing as of June 2009. These structures include gas stations, flowerbeds, cottages, restaurants, fountains and gateposts.
Glen Rose, Texas Glen Rose is a city in and the county seat of Somervell County, Texas, United States. As of the 2012 census estimate, the city population was 2,502. History 19th century The area was first settled in 1849 by Charles Barnard, who opened a tradin ...
is also noted for
Dinosaur Valley State Park Dinosaur Valley State Park is a state park near Glen Rose, Texas, United States. History Dinosaur Valley State Park, located just northwest of Glen Rose in Somervell County, Texas, is a scenic park set astride the Paluxy River. The land fo ...
and the
Glen Rose Formation The Glen Rose Formation is a shallow marine to shoreline geological formation from the lower Cretaceous period exposed over a large area from South Central to North Central Texas. The formation is most widely known for the dinosaur footprints ...
, where fossilized dinosaur footprints from the Cretaceous period can be viewed. Another example of the use of petrified wood in construction is the
Agate House Pueblo Agate House is a partially reconstructed Puebloan building in Petrified Forest National Park, built almost entirely of petrified wood. The eight-room pueblo has been dated to approximately the year 900 and occupied through 1200, of the Pueblo ...
in the
Petrified Forest National Park Petrified Forest National Park is an American national park in Navajo County, Arizona, Navajo and Apache County, Arizona, Apache counties in northeastern Arizona. Named for its large deposits of petrified wood, the park covers about , encompassin ...
in Arizona. Built by ancestral
Pueblo In the Southwestern United States, Pueblo (capitalized) refers to the Native tribes of Puebloans having fixed-location communities with permanent buildings which also are called pueblos (lowercased). The Spanish explorers of northern New Spain ...
people about 990 years ago, this eight-room building was constructed almost entirely out of petrified wood and is believed to have served as either a family home or ceremonial center.


Artificial petrifaction

In 2005 scientists at the Pacific Northwest National Laboratory (PNNL) reported that they had successfully petrified wood samples artificially. Unlike natural petrification, though, they infiltrated samples in acidic solutions, diffused them internally with
titanium Titanium is a chemical element with the symbol Ti and atomic number 22. Found in nature only as an oxide, it can be reduced to produce a lustrous transition metal with a silver color, low density, and high strength, resistant to corrosion in ...
and
carbon Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent In chemistry, the valence (US spelling) or valency (British spelling) of an element is the measure of its combining capacity with o ...
and fired them in a high-temperature oven (circa 1400 °C) in an inert atmosphere to yield a man-made ceramic matrix composite of
titanium carbide Titanium carbide, Ti C, is an extremely hard ( Mohs 9–9.5) refractory ceramic material, similar to tungsten carbide. It has the appearance of black powder with the sodium chloride ( face-centered cubic) crystal structure. It occurs in natur ...
and
silicon carbide Silicon carbide (SiC), also known as carborundum (), is a hard chemical compound containing silicon and carbon. A semiconductor, it occurs in nature as the extremely rare mineral moissanite, but has been mass-produced as a powder and crystal sin ...
still showing the initial structure of wood. Future uses would see these artificially petrified wood-ceramic materials eventually replace metal-based superalloys (which are coated with ultrahard ceramics) in the tool industry. Other vegetal matter could be treated in a similar process and yield abrasive powders. Scientists attempted to artificially petrify organisms as early as the 18th century, when
Girolamo Segato Girolamo Segato (13 June 1792 – 3 February 1836) was an Italian naturalist, cartographer, Egyptologist, and anatomist. He is perhaps best known for his work in the artificial petrifaction of human cadavers. Segato was born in the Carthusian ...
claimed to have supposedly "petrified" human remains. His methods were lost, but the bulk of his "pieces" are on display at the Museum of the Department of Anatomy in
Florence Florence ( ; it, Firenze ) is a city in Central Italy and the capital city of the Tuscany region. It is the most populated city in Tuscany, with 383,083 inhabitants in 2016, and over 1,520,000 in its metropolitan area.Bilancio demografico an ...
, Italy. More recent attempts have been both successful and documented, but should be considered as semi-petrifaction or incomplete petrifaction or at least as producing some novel type of wood composite, as the wood material remains to a certain degree; the constituents of wood (cellulose, lignins, lignans, oleoresins, etc.) have not been replaced by silicate, but have been infiltrated by specially formulated acidic solutions of aluminosilicate salts that gel in contact with wood matter and form a matrix of silicates within the
wood Wood is a porous and fibrous structural tissue found in the stems and roots of trees and other woody plants. It is an organic materiala natural composite of cellulose fibers that are strong in tension and embedded in a matrix of lignin th ...
after being left to react slowly for a given period of time in the solution or heat-cured for faster results. Hamilton Hicks of
Greenwich, Connecticut Greenwich (, ) is a New England town, town in southwestern Fairfield County, Connecticut, United States. At the 2020 United States Census, 2020 census, the town had a total population of 63,518. The largest town on Connecticut's Gold Coast (Conne ...
, received a patent for his "recipe" for rapid artificial petrifaction of wood under US patent 4,612,050 in 1986. Hicks' recipe consists of highly mineralized water and a sodium silicate solution combined with a dilute acid with a pH of 4.0-5.5. Samples of wood are penetrated with this mineral solution through repeated submersion and applications of the solution. Wood treated in this fashion is - according to the claims in the patent - incapable of being burned and acquires the features of petrified wood. Some uses of this product as suggested by Hicks include use by horse breeders who desire fireproof stables constructed of nontoxic material that would also be resistant to chewing of the wood by horses.


See also

*
Concretion A concretion is a hard, compact mass of matter formed by the precipitation of mineral cement within the spaces between particles, and is found in sedimentary rock or soil. Concretions are often ovoid or spherical in shape, although irregular ...
*
Petrifaction in mythology and fiction Petrifaction, or petrification, defined as turning people to stone, is a common theme in folklore and mythology, as well as in some works of modern literature. Amos Brown noted that "Fossils are to be found all over the world, a clear evidence to ...
*
Petrifying well A petrifying well is a well or other body of water which gives objects a stone-like appearance. If an object is placed into such a well and left there for a period of months or years, the object acquires a stony exterior. Nature If an object is p ...
*
Rhynie chert The Rhynie chert is a Lower Devonian sedimentary deposit exhibiting extraordinary fossil detail or completeness (a Lagerstätte). It is exposed near the village of Rhynie, Aberdeenshire, Scotland; a second unit, the Windyfield chert, is locate ...
* Substitution pseudomorph *
Taphonomy Taphonomy is the study of how organisms decay and become fossilized or preserved in the paleontological record. The term ''taphonomy'' (from Greek , 'burial' and , 'law') was introduced to paleontology in 1940 by Soviet scientist Ivan Efremov t ...


References

{{Reflist Botany Fossilization Sedimentary rocks