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Clinopyroxene thermobarometry is a
scientific method The scientific method is an empirical method for acquiring knowledge that has characterized the development of science since at least the 17th century (with notable practitioners in previous centuries; see the article history of scientific m ...
that uses the
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. ( ...
clinopyroxene to determine the
temperature Temperature is a physical quantity that expresses quantitatively the perceptions of hotness and coldness. Temperature is measured with a thermometer. Thermometers are calibrated in various temperature scales that historically have relied o ...
and
pressure Pressure (symbol: ''p'' or ''P'') is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled ''gage'' pressure)The preferred spelling varies by country and e ...
of the
magma Magma () is the molten or semi-molten natural material from which all igneous rocks are formed. Magma is found beneath the surface of the Earth, and evidence of magmatism has also been discovered on other terrestrial planets and some natural sa ...
when the mineral crystalized. Clinopyroxene is found in many
igneous rocks Igneous rock (derived from the Latin word ''ignis'' meaning fire), or magmatic rock, is one of the three main rock types, the others being sedimentary and metamorphic. Igneous rock is formed through the cooling and solidification of magma or ...
, so the method can be used to determine information about the entire rock. Many different minerals can be used for
geothermobarometry Geothermobarometry is the science of measuring the previous pressure and temperature history of a metamorphic or intrusive igneous rocks. Geothermobarometry is a combination of ''geobarometry'', where a pressure of mineral formation is resolved, an ...
, but clinopyroxene is especially useful because it's a common phenocryst in igneous rocks and easy to identify, and the crystallization of
jadeite Jadeite is a pyroxene mineral with composition sodium, Naaluminium, Alsilicon, Si2oxygen, O6. It is hard (Mohs hardness of about 6.5 to 7.0), very tough, and dense, with a specific gravity of about 3.4. It is found in a wide range of colors, bu ...
, a type of clinopyroxene, implies a growth in molar volume, making it a good indicator of pressure. The data given by this technique is used for understanding magmatic
crystallization Crystallization is the process by which solid forms, where the atoms or molecules are highly organized into a structure known as a crystal. Some ways by which crystals form are precipitating from a solution, freezing, or more rarely deposi ...
, prograde and retrograde
metamorphism Metamorphism is the transformation of existing rock (the protolith) to rock with a different mineral composition or texture. Metamorphism takes place at temperatures in excess of , and often also at elevated pressure or in the presence of chem ...
, and ore deposit formation. Understanding these processes can aid industries as well as the scientific community. With this data, information about the
lithosphere A lithosphere () is the rigid, outermost rocky shell of a terrestrial planet or natural satellite. On Earth, it is composed of the crust (geology), crust and the portion of the upper mantle (geology), mantle that behaves elastically on time sca ...
composition can be extrapolated in more detail, and the
diamond Diamond is a Allotropes of carbon, solid form of the element carbon with its atoms arranged in a crystal structure called diamond cubic. Another solid form of carbon known as graphite is the Chemical stability, chemically stable form of car ...
exploration industry can determine the probability that a kimberlite contains diamonds.{{Cite journal, last=Grütter, first=Herman S., date=2009, title=Pyroxene xenocyst geotherms: Techniques and Application, journal=Lithos, volume=112, pages=1167-1178, doi=10.1016/j.lithos.2009.03.023


Methods

Thermobarometry Geothermobarometry is the science of measuring the previous pressure and temperature history of a metamorphic or intrusive igneous rocks. Geothermobarometry is a combination of ''geobarometry'', where a pressure of mineral formation is resolved, an ...
uses
equilibrium constants The equilibrium constant of a chemical reaction is the value of its reaction quotient at chemical equilibrium, a state approached by a dynamic chemical system after sufficient time has elapsed at which its composition has no measurable tendency ...
to calculate information about the environmental conditions present during the rocks' formation. While each rock is forming, it
reacts ''React'' (from Spanish: ''Reacciona'') is a book by Rosa María Artal published in Spain in 2011 by Aguilar, which compiles articles by José Luis Sampedro, Baltasar Garzón, Federico Mayor Zaragoza, Javier Pérez de Albéniz, Javier López Facal ...
with the surrounding elements until it cools down enough to become inert. Each mineral within the rock will cool and crystalize at different points; a
petrogenetic grid A petrogenetic grid is a geological phase diagram that connects the stability ranges or metastability ranges of metamorphic minerals or mineral assemblages to the conditions of metamorphism. Experimentally determined mineral or mineral-assembla ...
is a useful way to visualize each mineral crystalizing in sequence. Individual reactions of specific minerals can be used to calculate either the temperature or pressure. Therefore, two different reactions are needed to calculate both the temperature and pressure of the magma for a single rock. Some reactions are better for pressure and others are better for temperature, based on
thermodynamics Thermodynamics is a branch of physics that deals with heat, work, and temperature, and their relation to energy, entropy, and the physical properties of matter and radiation. The behavior of these quantities is governed by the four laws of the ...
and Le Chatelier's Principle. This technique requires each reaction to be calibrated, which is done through experimentation and
data analysis Data analysis is a process of inspecting, cleansing, transforming, and modeling data with the goal of discovering useful information, informing conclusions, and supporting decision-making. Data analysis has multiple facets and approaches, enco ...
. Experimentation involves simulating the temperatures and pressures at which these rocks form and observing how the reaction proceeds at those conditions, while data analysis relies on amassing a large
database In computing, a database is an organized collection of data stored and accessed electronically. Small databases can be stored on a file system, while large databases are hosted on computer clusters or cloud storage. The design of databases sp ...
of rock samples with pressure and temperature information. Experimental data tends to have significant variation, so using data from natural formations is more
accurate Accuracy and precision are two measures of '' observational error''. ''Accuracy'' is how close a given set of measurements ( observations or readings) are to their ''true value'', while ''precision'' is how close the measurements are to each ot ...
, if it's available.


Pressure

The reactions best for pressure ( geobarometers) are ones that have a large change in molar volume during the reaction. Higher pressures cause the reaction to decrease in total volume, and lighter pressures allow reaction to increase in total volume. Therefore, based on the proportion of minerals that have larger volumes versus the proportion of minerals that have smaller volumes, the pressure of the environment during the reaction can be calculated, as a function of temperature. Experiments must be done to calibrate each reaction and determine the rate at which the volume changes with changes in pressure.


Temperature

The reactions best for temperature ( geothermometers) are ones that have a large
enthalpy Enthalpy , a property of a thermodynamic system, is the sum of the system's internal energy and the product of its pressure and volume. It is a state function used in many measurements in chemical, biological, and physical systems at a constant ...
of reaction, which means they release or consume a lot of
heat In thermodynamics, heat is defined as the form of energy crossing the boundary of a thermodynamic system by virtue of a temperature difference across the boundary. A thermodynamic system does not ''contain'' heat. Nevertheless, the term is al ...
. Higher temperatures allow the reaction to consume that heat while lower temperatures cause the reaction to release heat. Similarly to geobarometers, the proportion of minerals that are formed by releasing heat versus consuming heat can be used to calculate the temperature, as long as the reaction is calibrated.


Reaction Types

There are three types of reactions that clinopyroxene is involved in and can be used for thermobarometry. ''Univariant reactions or displaced equilibria reactions'' either create or destroy phases within the magma. Each phase will eventually crystalize as a unique mineral. Based on the temperature and pressure conditions, different proportions of these phases will emerge in the final rock. An example reaction is
jadeite Jadeite is a pyroxene mineral with composition sodium, Naaluminium, Alsilicon, Si2oxygen, O6. It is hard (Mohs hardness of about 6.5 to 7.0), very tough, and dense, with a specific gravity of about 3.4. It is found in a wide range of colors, bu ...
and
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 ...
reacting to make analbite. Jadeite is a type of
pyroxene The pyroxenes (commonly abbreviated to ''Px'') are a group of important rock-forming inosilicate minerals found in many igneous and metamorphic rocks. Pyroxenes have the general formula , where X represents calcium (Ca), sodium (Na), iron (Fe II) ...
, so this reaction is used for clinopyroxene barometry. NaAlS2O6 + SiO2 -> NaAlS3O8 This particular reaction involves a large change in
volume Volume is a measure of occupied three-dimensional space. It is often quantified numerically using SI derived units (such as the cubic metre and litre) or by various imperial or US customary units (such as the gallon, quart, cubic inch). The de ...
between the
reactants In chemistry, a reagent ( ) or analytical reagent is a substance or compound added to a system to cause a chemical reaction, or test if one occurs. The terms ''reactant'' and ''reagent'' are often used interchangeably, but reactant specifies a ...
and the products, so the reaction is very sensitive to pressure changes. ''Exchange Reactions'' occur when there are minerals with similar structures, and ions switch places with each other within that structure. This is a common method to calculate the temperature because most exchange reactions have a high
enthalpy Enthalpy , a property of a thermodynamic system, is the sum of the system's internal energy and the product of its pressure and volume. It is a state function used in many measurements in chemical, biological, and physical systems at a constant ...
. One example reaction is an exchange of Fe2+ and Mg2+ within
garnet Garnets () are a group of silicate minerals that have been used since the Bronze Age as gemstones and abrasives. All species of garnets possess similar physical properties and crystal forms, but differ in chemical composition. The different s ...
and clinopyroxene. That causes
pyrope The mineral pyrope is a member of the garnet group. Pyrope is the only member of the garnet family to always display red colouration in natural samples, and it is from this characteristic that it gets its name: from the Greek for ''fire'' and ''e ...
and hedenbergite (pyroxene) to change into
almandine Almandine (), also known as almandite, is a species of mineral belonging to the garnet group. The name is a corruption of alabandicus, which is the name applied by Pliny the Elder to a stone found or worked at Alabanda, a town in Caria in Asia M ...
and diopside (pyroxene). Mg3Al2Si3O12 + 3CaFeSi2O6 -> Fe3Al2Si3O12 + 3CaMgSi2O6 ''Solvus Equilibria'' reactions occur when two phases dissolve into each other based on the temperature, so it is usually useful for geothermometry. One such reaction is when clinopyroxene and
orthopyroxene The pyroxenes (commonly abbreviated to ''Px'') are a group of important rock-forming inosilicate minerals found in many igneous and metamorphic rocks. Pyroxenes have the general formula , where X represents calcium (Ca), sodium (Na), iron (Fe II) ...
dissolve into each other. This changes the distribution of
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 to ...
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 ...
throughout the mineral.


Applications

Clinopyroxene thermobarometry is usually used by
mining Mining is the extraction of valuable minerals or other geological materials from the Earth, usually from an ore body, lode, vein, seam, reef, or placer deposit. The exploitation of these deposits for raw material is based on the economic via ...
industries. It is particularly helpful to the
diamond Diamond is a Allotropes of carbon, solid form of the element carbon with its atoms arranged in a crystal structure called diamond cubic. Another solid form of carbon known as graphite is the Chemical stability, chemically stable form of car ...
industry, so many stakeholders possess pressure and temperature data regarding the formation of rocks that contain diamonds. This is important because diamonds are usually found in kimberlites, but kimberlites do not always contain diamonds. Instead of mining every kimberlite found, they can be sampled to see if they formed in an environment that would have favored the crystallization of diamonds. Other applications are largely scientific; pressure and temperature data about magma can be used to propose detailed
models A model is an informative representation of an object, person or system. The term originally denoted the plans of a building in late 16th-century English, and derived via French and Italian ultimately from Latin ''modulus'', a measure. Models c ...
of the
lithosphere A lithosphere () is the rigid, outermost rocky shell of a terrestrial planet or natural satellite. On Earth, it is composed of the crust (geology), crust and the portion of the upper mantle (geology), mantle that behaves elastically on time sca ...
and mantle. These models enhance understanding of geological and volcanic activity, which may contribute to scientists' ability to predict events such as eruptions or
earthquakes An earthquake (also known as a quake, tremor or temblor) is the shaking of the surface of the Earth resulting from a sudden release of energy in the Earth's lithosphere that creates seismic waves. Earthquakes can range in intensity, from ...
.


References

Geochemistry Igneous rocks Geologic modelling