Breyite

breyite

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Formula: Ca₃Si₃O₉
Cyclosilicate (ring silicate), margarosanite group, high pressure triclinic paramorph of isometric davemaoite, monoclinic pseudowollastonite and triclinic wollastonite
Crystal System: Triclinic
Specific gravity: 3.072 calculated
Colour: Colourless
Luminescence: Not fluorescent under UV
Environments

Derived from Earth's Mantle

Localities

The type locality is the São Luis river alluvials, Juína, Mato Grosso, Brazil.
Earth’s lower mantle most likely mainly consists of ferropericlase, bridgmanite, and a CaSiO₃ phase in the perovskite structure. If separately trapped in diamonds, these phases can be transported to Earth’s surface without reacting with the surrounding mantle. Although all inclusions will remain chemically pristine, only ferropericlase will stay in its original crystal structure, whereas in almost all cases bridgmanite and CaSiO₃-perovskite will transform to their lower-pressure polymorphs. In the case of perovskite structured CaSiO₃, the new structure that is formed is closely related to that of walstromite. This mineral is now approved by the IMA and named breyite.
Breyite is the second most abundant mineral inclusion after ferropericlase in diamonds of super-deep origin. The occurrence of breyite has been widely presumed to be a strong indication of lower mantle (>670 km depth) or at least lower transition zone (>520 km depth) origin of both the host diamond and the inclusion suite. However, the finding of breyite alone in a diamond is not a reliable indicator of the formation depth in the transition zone or in the lower mantle, and accompanying paragenetic phases such as ferropericlase together with MgSiO₃ are needed. (AM 106.1.38-43).
Minerals associated with breyite include diamond, ferropericlase, CaTiO₃-perovskite, β-Ca₂SiO₄ larnite, titanite-structured CaSi₂O₅ and ringwoodite (HOM).

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