Experimental petrology is the field of research concerned with experimentally determining the physical and chemical behavior of

rocks In geology, rock (or stone) is any naturally occurring solid mass or aggregate of minerals or mineraloid matter. It is categorized by the minerals included, its chemical composition, and the way in which it is formed. Rocks form the Earth's ...

and their constituents. Because there is no way to directly observe or measure deep earth processes, geochemists rely on experimental

petrology Petrology () is the branch of geology that studies rocks and the conditions under which they form. Petrology has three subdivisions: igneous, metamorphic, and sedimentary petrology. Igneous and metamorphic petrology are commonly taught together ...

to establish quantitative values and relationships in order to construct models of the deep earth. Experimental petrology can range from creating artificial

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 ...

s to measure

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 ...

behavior to observing recrystallization of

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 at varying pressure/temperature conditions.

Methodology

Although methodology varies from experiment to experiment, in general the procedure involves evaluating a synthetic rock or

(created from a blend of oxides to replicate the chemistry of the rock/system in question) in an apparatus capable of creating and sustaining high pressures and temperatures such as a

diamond anvil cell A diamond anvil cell (DAC) is a high-pressure device used in geology, engineering, and materials science experiments. It enables the compression of a small (sub-millimeter-sized) piece of material to extreme pressures, typically up to around 10 ...

. In general, it is ideal if the enclosing capsule is relatively nonreactive, such as diamond or platinum/gold alloys.

Experimental igneous petrology

Experimental igneous petrology is the subset of experimental petrology concerned with quantifying the behavior of magmas and their associated igneous rocks at depth. Standard procedure generally involves the creation of a synthetic magma (often corresponding to a real world analog) which is then cooled to a target temperature. After crystallization, the products are analyzed - qualities of interest include mineral assemblage (which minerals crystallized and how much), mineral chemistry, and liquid (the remainder of the synthetic magma base) composition.

Equilibrium crystallization

Equilibrium crystallization studies are those in which a starting liquid is cooled until fully crystalline. This is taken to be the "equilibrium state" of the composition under those particular P/T conditions. Criticisms of equilibrium crystallization include the observation that real-world systems are believed to rarely sit still during crystallization and thus would not be able to properly equilibrate.

Fractional crystallization

Fractional crystallization studies represent a fairly recent trend in experimental petrology, gaining popularity as a way to more accurately depict magma evolution in scenarios where a

cumulate Cumulate rocks are igneous rocks formed by the accumulation of crystals from a magma either by settling or floating. Cumulate rocks are named according to their texture; cumulate texture is diagnostic of the conditions of formation of this group o ...

layer is built. In them, a starting liquid is cooled in small temperature steps (e.g. 30 °C). At each temperature step the contents are removed and analyzed as in equilibrium crystallization. Afterwards, a new liquid corresponding to the residual liquid from the previous step is synthesized, heated, and then subjected to another cooling step. The purpose of this stepwise approach is to examine how each new interval of crystallization affects the chemistry of the parent magma and, thus, the behavior of future crystallization steps. In such a manner it is possible to examine the behavior of a magma body as it slowly cools and crystallizes over time.

References

{{reflist Petrology

Methodology

Experimental igneous petrology

Equilibrium crystallization

Fractional crystallization

See also

References