Hemleyite

Chemical formula: Fe<sup>₂+</sup>SiO<sub>₃</sub>

Hemleyite is a high-pressure iron silicate polymorph with a perovskite structure, found in shocked meteorites.

## Characteristics Hemleyite is an extremely rare mineral from the perovskite group, representing a high-pressure polymorphic variety of iron(II) silicate. It occurs as submicroscopic grains or lamellae, usually less than one micrometer in size. Due to its size, its visual characteristics cannot be observed with the naked eye or under a standard optical microscope. When observed in reflected light under an electron microscope, it is black and opaque. ## Physical Properties Hemleyite crystals are too small to determine their hardness or fracture. The density of the mineral, calculated based on unit cell parameters, is approximately 5.17 g/cm³. It exhibits a submetallic luster. It is a completely opaque mineral. ## Colors and Varieties The mineral is black. No colored or commercial varieties are known. ## History and Name Hemleyite was officially recognized by the International Mineralogical Association (IMA) in 2017 under the number IMA2017-088. Its name honors Russell J. Hemley, an American geophysicist and pioneer in the field of matter research under extremely high pressure. The mineral was first identified in shock veins within the Tenham meteorite, which fell in Australia. ## Applications Hemleyite has no commercial or industrial applications. Its significance is purely scientific, as its occurrence provides key information about the extreme pressure and temperature conditions prevailing during meteorite impacts and, potentially, in the deep parts of the Earth's mantle.

Properties

Luster: Submetallic
Density: 5.17
Transparency: Opaque
Crystal system: Orthorhombic

Diagnostic features

## Identification Identification of hemleyite is impossible without advanced analytical techniques. It requires the use of electron microscopy (SEM), electron microprobe analysis (EMPA) for chemical composition, and X-ray diffraction (XRD) or electron diffraction to confirm its unique, perovskite crystal structure. It cannot be visually identified. ## Distinguishing from Similar Minerals Hemleyite must be distinguished from other FeSiO₃ polymorphs, such as ferrosilite (with a pyroxene structure), which forms under lower pressure conditions. Within shock veins in meteorites, it coexists with bridgmanite ((Mg,Fe)SiO₃), from which it is distinguished by the dominance of iron over magnesium. Differentiation is based solely on structural and chemical analysis. ## Crystal Forms It forms submicroscopic, tabular or platy crystals, often arranged as lamellar intergrowths within bridgmanite or ringwoodite crystals. It also occurs as fine, irregular grains in aggregates.

Geological environment

## Genesis Hemleyite is a high-pressure mineral, forming under conditions of extreme pressure (above 20 GPa) and high temperature. Such conditions occur naturally during high-velocity meteorite impacts, leading to shock metamorphism. It is also believed that a phase with the hemleyite structure may be a significant component of the Earth's lower mantle. ## Mineral Associations This mineral occurs in paragenesis with other high-pressure minerals within shock veins in meteorites. It is most commonly associated with bridgmanite, ringwoodite, akimotoite, as well as majorite, magnesiowüstite, and metallic iron-nickel alloys (kamacite, taenite). ## Localities Its occurrence has been confirmed in several shocked ordinary chondrites of the L6 type. The type locality is the Tenham meteorite, found in Queensland, Australia. Another confirmed locality is the Suizhou meteorite, which fell in Hubei Province, China.

Rarity

Extremely rare

For collectors

## Quality Criteria Traditional criteria for evaluating specimens do not apply to hemleyite. The collectible and scientific value lies in the mere presence of this mineral in a meteorite specimen, confirmed by research. The most valuable objects are polished thin sections of the meteorite, where shock veins containing hemleyite can be identified under a microscope. ## Popular Localities The only sources for obtaining specimens containing hemleyite are the finding or fall sites of meteorites where it has been identified. The most important of these are the Tenham Station area in Australia and the vicinity of Suizhou in China.

Care and storage

## Cleaning Cleaning individual hemleyite crystals is impossible due to their microscopic size and occurrence as inclusions. Care applies only to the parent specimen (meteorite). ## What to Avoid Meteorite specimens containing hemleyite should be protected from moisture, which can cause rusting of metallic phases and degradation of the entire sample. Contact with chemicals, extreme temperatures, and ultrasound should be avoided. ## Storage Meteorites with hemleyite are best stored in a dry environment, preferably in a container with a desiccant (desiccator) or in a sealed display case. This prevents slow oxidation and breakdown of the minerals within the specimen.

Sources

IMA Mineral List (CNMNC)