Wadsleyite

Chemical formula: Mg<sub>2</sub>SiO<sub>4</sub>

Wadsleyite is a high-pressure polymorph of olivine, a key mineral of Earth's upper mantle, found mainly in meteorites.

## Characteristics Wadsleyite is a high-pressure polymorph of olivine, formed under conditions prevailing in the Earth's mantle, at depths of 410 to 520 km. In nature, on the Earth's surface, it is found almost exclusively in heavily shocked meteorites, where it forms as a result of impact. This mineral is typically microscopic in size, forming aggregates of fine grains replacing primary olivine. Due to its origin and formation conditions, well-formed crystals visible to the naked eye are extremely rare and are only found in laboratory experiments. ## Physical Properties Synthetic wadsleyite crystals exhibit a hardness of approximately 7 on the Mohs scale. The mineral is characterized by a vitreous luster and is typically transparent to translucent. Its density is about 3.84 g/cm³, which is significantly higher than that of olivine, reflecting the denser atomic packing in its crystal structure. ## Colors and Varieties The color of wadsleyite depends on impurities. The pure, synthetic form (Mg₂SiO₄) is colorless. Naturally occurring iron-bearing wadsleyite in meteorites ranges in color from pale green to olive green. No commercial or color varieties are distinguished. ## History and Name The mineral was named in honor of Arthur David Wadsley (1918-1969), an Australian crystal chemist who made significant contributions to understanding the structures of transition metal oxides. It was first identified in nature in 1982 in the Tenham meteorite, which fell in Queensland, Australia. However, its existence was theoretically predicted and experimentally confirmed in high-pressure laboratories as early as the 1960s. ## Applications Wadsleyite has no industrial or commercial applications. Its significance is purely scientific – it is a key mineral for geophysicists and geochemists studying the composition and dynamics of Earth's interior, particularly the mantle transition zone. For collectors, it represents a unique, though usually microscopic, object of interest, mainly in the context of meteorite collecting.

Properties

Mohs hardness
7
Luster
Vitreous
Streak
White
Density
3.84
Cleavage
Perfect on {010}, good on {001}
Fracture
Uneven
Transparency
Transparent to translucent
Crystal system
Orthorhombic

Diagnostic features

## Identification Identification of wadsleyite is impossible without advanced laboratory techniques such as X-ray diffraction (XRD), electron microscopy (SEM/TEM), or Raman spectroscopy. In practice, it is recognized based on its geological context – its presence in heavily shocked chondrites (stony meteorites), where it forms veins or aggregates replacing olivine. ## Distinguishing from Similar Minerals Visually, in thin sections under a microscope, it can resemble olivine or ringwoodite (another high-pressure polymorph of olivine). Differentiation from olivine requires analysis of optical properties (higher refractive indices) or structural properties. Ringwoodite, crystallizing in the isometric system, is optically isotropic, which distinguishes it from anisotropic wadsleyite. ## Crystal Forms In nature, it occurs exclusively as microscopic, anhedral (irregularly shaped) grains forming dense aggregates. Synthetic crystals obtained under laboratory conditions can form small, platy or prismatic shapes, but these are not found in natural specimens.

Geological environment

## Genesis Wadsleyite is a high-pressure mineral. Its primary formation environment is the transition zone of Earth's upper mantle, at depths of 410-520 km, where it forms as a result of the phase transformation of olivine under pressures of approximately 14-18 GPa. It is not transported to the Earth's surface, as it transforms back into olivine under lower pressure conditions. The only known natural mechanism for its preservation on the surface is meteorite impact. In such cases, shock pressure and temperature briefly recreate conditions from the Earth's mantle, transforming olivine within the meteorite into wadsleyite and ringwoodite, which are then rapidly cooled, thus "freezing" their structure. ## Mineral Associations In meteorites, wadsleyite coexists with minerals from which it formed or with which it was associated, mainly olivine, pyroxenes, plagioclase (or its high-pressure forms like maskelynite), troilite, iron-nickel alloy, and other shock minerals such as ringwoodite, akimotoite, and majorite. ## Localities Confirmed occurrences of wadsleyite are limited to heavily shocked meteorites. Key examples include the Tenham meteorite (Queensland, Australia), Peace River (Alberta, Canada), Sixiangkou (China), and Tissint (Morocco).

Rarity

Extremely rare

For collectors

## Quality Criteria The quality of a specimen containing wadsleyite is practically identical to the quality of the host meteorite itself. For collectors and scientific institutions, the primary concern is the confirmation of the mineral's presence through analysis. Value is enhanced by well-documented provenance of the specimen and clear shock textures visible in cut and polished fragments (so-called "slices"), where wadsleyite veins may appear as darker areas. The size of these veins and aggregates is also important, although they rarely exceed millimeters. ## Popular Localities The most well-known and prized specimens come from classic localities where this mineral or its best examples were first identified. These include the Tenham and Peace River meteorites. Specimens from these localities are extremely rare on the commercial market and are primarily found in institutional and research collections.

Care and storage

## Cleaning Specimens (usually meteorite fragments) containing wadsleyite should be handled with the utmost care. Cleaning should be kept to an absolute minimum. If necessary, compressed air can be used to remove dust. Avoid contact with water and chemicals that could damage the meteorite matrix. ## What to Avoid Ultrasonic cleaners, chemical agents, acids, and sudden temperature changes should be absolutely avoided. As a high-pressure mineral, it is metastable under Earth's surface conditions and theoretically can transform back into olivine under high temperatures, although this process is very slow. ## Storage Specimens should be stored in stable, dry conditions, away from direct sunlight and heat sources. It is best to store them in padded boxes or display cases to minimize the risk of mechanical damage and vibrations.

External references

Sources

Read more