Bridgmanite

Chemical formula: MgSiO₃

Bridgmanite is the most abundant mineral on Earth, forming the main component of the planet's lower mantle, and its natural specimens are found exclusively in meteorites.

## Characteristics Bridgmanite, a magnesium silicate with a perovskite structure, is recognized as the most abundant mineral in the entire mass of the Earth, constituting approximately 70% of the volume of its lower mantle. Despite its omnipresence within the planet, it is extremely rare on the surface. Natural samples of bridgmanite have so far only been identified as microscopic grains within some stony meteorites (chondrites) that underwent thermal and pressure shock during atmospheric entry or collisions in space. These grains are too small to be observed with the naked eye. ## Physical Properties Due to its occurrence as microscopic inclusions, most physical properties of bridgmanite, such as luster, transparency, or hardness, are determined based on synthetic material or theoretical calculations. Research indicates that it is a material of high density and hardness, which corresponds to the conditions prevailing in the Earth's lower mantle. ## Colors and Varieties Natural bridgmanite observed in meteorites is typically colorless or has very light hues. Studies of synthetic counterparts suggest that the presence of iron ions, which can substitute for magnesium in the crystal structure, affects its color and properties; however, no formal varieties of this mineral are distinguished. ## History and Name The existence of a high-pressure polymorph of magnesium silicate in the Earth's mantle had been postulated for decades, but its confirmation in nature was impossible due to a lack of samples. The mineral was officially recognized and named in 2014 in honor of Percy Bridgman (1882–1961), a Nobel Prize laureate in physics in 1946 for his pioneering research on high-pressure physics. The discovery was made based on the analysis of grains in the Tenham meteorite, which fell in Australia in 1879. ## Uses Bridgmanite has no commercial or industrial applications. Its significance is purely scientific, serving as a key to understanding the composition, structure, and dynamics of the Earth's interior. It is the subject of intensive research in geophysics and materials science.

Properties

Crystal system: Orthorhombic

Diagnostic features

## Identification Identification of bridgmanite is impossible without advanced laboratory techniques. It requires the use of a scanning electron microscope (SEM) with EDS analysis to determine chemical composition and electron or X-ray diffraction (XRD) to confirm the perovskite crystal structure. In collector practice, identification is unfeasible. ## Distinguishing from Similar Minerals Bridgmanite occurs in association with other high-pressure minerals in meteorite shock veins, such as ringwoodite and majorite. Distinguishing them from each other relies solely on precise analysis of composition and crystal structure in the laboratory. ## Crystal Forms Bridgmanite forms submicron, anhedral (lacking well-formed faces) grains or polycrystalline aggregates within veins formed as a result of shock metamorphism in meteorites.

Geological environment

## Genesis Bridgmanite is a high-pressure mineral. Under terrestrial conditions, it crystallizes in the lower mantle at depths from approximately 660 km to 2900 km, under pressures from 23 to 136 GPa and temperatures exceeding 1700°C. It forms as a result of the phase transformation of other magnesium silicates, primarily ringwoodite. The only natural samples available on Earth's surface come from chondrites that experienced extremely high pressure and temperature during collisions in the asteroid belt or atmospheric entry. ## Mineral Associations On Earth, bridgmanite coexists with ferropericlase in the lower mantle. In meteorites (e.g., Tenham, Suizhou), it is found in shock veins along with other high-pressure minerals such as ringwoodite, majorite, akimotoite, as well as olivine, pyroxene, and metallic alloy (kamacite, taenite). ## Localities As a mineral defining Earth's interior, bridgmanite occurs globally in the lower mantle. The only confirmed localities from which natural samples for research have been obtained are the meteorites in which it was identified. The type locality is the Tenham meteorite (Queensland, Australia). Other known occurrences include the Suizhou (China) and Tissint (Morocco) meteorites.

Rarity

Extremely rare

For collectors

## Quality Criteria Bridgmanite is not a collector's mineral in the traditional sense. Its value is purely scientific and historical. Specimens are, in reality, fragments of meteorites in which the presence of microscopic bridgmanite grains has been confirmed. The appeal of such a specimen depends on its provenance, research history, and the quality of the meteorite itself (size, type, state of preservation). Owning a meteorite fragment with confirmed bridgmanite is a rarity for specialized institutional collections or very advanced private collectors. ## Popular Localities The most famous and historically most important "locality" is the Tenham meteorite from Australia, as it was the first in which natural bridgmanite was identified and described. Other meteorites, such as Suizhou, are also important sources of material for scientific research.

Care and storage

## Cleaning Bridgmanite specimens occur as microscopic inclusions within the meteorite matrix. They are not cleaned directly. Any cleaning pertains to the entire meteorite specimen and should be limited to an absolute minimum, e.g., removing loose dust with a soft brush or compressed air from a safe distance. ## What to Avoid Avoid all chemicals, water, and ultrasonics, as they can damage both the delicate meteorite matrix and the inclusions themselves. Meteorites, especially chondrites, are sensitive to moisture, which can lead to their oxidation and disintegration. ## Storage Meteorite specimens containing bridgmanite must be stored under controlled, low-humidity conditions. It is best to use specialized boxes with a membrane or airtight containers with a desiccant (e.g., silica gel). Avoid abrupt temperature changes and direct sunlight.