Silicate perovskite is either (the magnesium end-member is called bridgmanite) or (

calcium silicate Calcium silicate can refer to several silicates of calcium including: *CaO·SiO2, wollastonite (CaSiO3) *2CaO·SiO2, larnite (Ca2SiO4) *3CaO·SiO2, alite or (Ca3SiO5) *3CaO·2SiO2, (Ca3Si2O7). This article focuses on Ca2SiO4, also known as calci ...

known as davemaoite) when arranged in a perovskite structure. Silicate perovskites are not stable at Earth's surface, and mainly exist in the lower part of Earth's mantle, between about depth. They are thought to form the main mineral phases of the lower mantle, together with ferropericlase.

Discovery

The existence of silicate perovskite in the mantle was first suggested in 1962, and both and had been synthesized experimentally before 1975. By the late 1970s, it had been proposed that the seismic discontinuity at about 660 km in the mantle represented a change from spinel structure minerals with an

olivine The mineral olivine () is a magnesium iron Silicate minerals, silicate with the chemical formula . It is a type of Nesosilicates, nesosilicate or orthosilicate. The primary component of the Earth's upper mantle (Earth), upper mantle, it is a com ...

composition to silicate perovskite with ferropericlase. Natural silicate perovskite was discovered in the heavily shocked Tenham meteorite. In 2014, the Commission on New Minerals, Nomenclature and Classification (CNMNC) of the

International Mineralogical Association Founded in 1958, the International Mineralogical Association (IMA) is an international group of 40 national societies. The goal is to promote the science of mineralogy and to standardize the nomenclature of the 5000 plus known mineral species. ...

(IMA) approved the name bridgmanite for perovskite-structured , in honor of

physicist A physicist is a scientist who specializes in the field of physics, which encompasses the interactions of matter and energy at all length and time scales in the physical universe. Physicists generally are interested in the root or ultimate cau ...

Percy Bridgman, who was awarded the

Nobel Prize in Physics The Nobel Prize in Physics () is an annual award given by the Royal Swedish Academy of Sciences for those who have made the most outstanding contributions to mankind in the field of physics. It is one of the five Nobel Prizes established by the ...

in 1946 for his high-pressure research. In 2021 perovskite-structured was found as an inclusion in a natural diamond. The name davemaoite has been adopted for this mineral.

Structure

The perovskite structure (first identified in the mineral perovskite) occurs in substances with the general formula , where A is a metal that forms large

cation An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convent ...

s, typically

magnesium Magnesium is a chemical element; it has Symbol (chemistry), 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 ...

, ferrous iron, or

calcium Calcium is a chemical element; it has 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 it ...

. B is another metal that forms smaller cations, typically

silicon Silicon is a chemical element; it has symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic lustre, and is a tetravalent metalloid (sometimes considered a non-metal) and semiconductor. It is a membe ...

, although minor amounts of ferric iron and

aluminum Aluminium (or aluminum in North American English) is a chemical element; it has chemical symbol, symbol Al and atomic number 13. It has a density lower than that of other common metals, about one-third that of steel. Aluminium has ...

can occur. X is typically oxygen. The structure may be cubic, but only if the relative sizes of the ions meet strict criteria. Typically, substances with the perovskite structure show lower symmetry, owing to the distortion of the crystal lattice and silicate perovskites are in the

orthorhombic crystal system In crystallography, the orthorhombic crystal system is one of the 7 crystal systems. Orthorhombic lattices result from stretching a cubic lattice along two of its orthogonal pairs by two different factors, resulting in a rectangular prism with ...

Occurrence

Stability range

Bridgmanite is a high-pressure polymorph of enstatite, but in the

Earth Earth is the third planet from the Sun and the only astronomical object known to Planetary habitability, harbor life. This is enabled by Earth being an ocean world, the only one in the Solar System sustaining liquid surface water. Almost all ...

predominantly forms, along with ferropericlase, from the decomposition of ringwoodite (a high-pressure form of

) at approximately 660 km depth, or a pressure of about 24 GPa. The depth of this transition depends on the mantle temperature; it occurs slightly deeper in colder regions of the mantle and shallower in warmer regions. The transition from ringwoodite to bridgmanite and ferropericlase marks the bottom of the mantle transition zone and the top of the lower mantle. Bridgmanite becomes unstable at a depth of approximately 2700 km, transforming isochemically to post-perovskite. Calcium silicate perovskite is stable at slightly shallower depths than bridgmanite, becoming stable at approximately 500 km, and remains stable throughout the lower mantle.

Abundance

Bridgmanite is the most abundant mineral in the mantle. The proportions of bridgmanite and calcium perovskite depends on the overall lithology and bulk composition. In pyrolitic and harzburgitic lithologies, bridgmanite constitutes around 80% of the mineral assemblage, and calcium perovskite less than 10%. In an eclogitic lithology, bridgmanite and calcium perovskite comprise about 30% each. Magnesium silicate perovskite is probably the most abundant mineral phase in the Earth.

Presence in diamonds

Calcium silicate perovskite has been identified at Earth's surface as inclusions in diamonds. The diamonds are formed under high pressure deep in the mantle. With the great mechanical strength of the diamonds a large part of this pressure is retained inside the lattice, enabling inclusions such as the calcium silicate to be preserved in high-pressure form.

Deformation

Experimental deformation of polycrystalline under the conditions of the uppermost part of the lower mantle suggests that silicate perovskite deforms by a dislocation creep mechanism. This may help explain the observed seismic anisotropy in the mantle.

References

External links

* * * * {{Minerals Petrology Silicate minerals Perovskites High pressure science Earth's mantle