Ringwoodite

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

Ringwoodite is a high-pressure polymorph of olivine, occurring naturally in the Earth's mantle, and found on the surface primarily in meteorites.

## Characteristics Ringwoodite is a silicate mineral, a high-pressure polymorphic variety of forsterite (Mg₂SiO₄), the main component of olivine. Under conditions prevailing deep within the Earth's mantle (transition zone, 520-660 km depth), it is one of the dominant minerals. On the Earth's surface, it is extremely rare. Found specimens are most often microscopic grains in chondritic meteorites that have undergone shock metamorphism during collisions in space. In 2014, it was identified as an inclusion in diamonds originating from the deep mantle, providing the first direct evidence of the presence of water in this zone of the Earth. ## Physical Properties This mineral is characterized by high hardness, approximately 6 on the Mohs scale. Its luster is typically vitreous. It is a transparent to translucent mineral. The density of ringwoodite, approximately 3.9 g/cm³, is significantly higher than that of olivine, which is a result of the "packing" of the crystal structure under extreme pressure. ## Colors and Varieties Synthetic ringwoodite is colorless. Natural specimens, depending on impurities and conditions, can take on various colors – from purple, blue, gray to greenish. No named commercial or gemological varieties are distinguished due to the extreme rarity and microscopic size of natural crystals. ## History and Name The mineral is named in honor of Alfred "Ted" Ringwood (1930-1993), an Australian geochemist and experimental petrologist, who predicted the existence of this polymorphic phase of olivine in the Earth's mantle. The mineral was first identified in nature in 1969 in the Tenham meteorite, which fell in Australia (Queensland) in 1879. ## Uses Ringwoodite has no commercial or industrial applications. Its significance is purely scientific, as a key mineral for understanding processes occurring deep within the Earth's mantle, including the global water cycle.

Properties

Mohs hardness
6
Luster
Vitreous
Streak
White
Density
3.90
Cleavage
None
Fracture
Uneven
Transparency
Transparent to translucent
Crystal system
Cubic

Diagnostic features

## Identification Identification of ringwoodite is impossible without advanced laboratory techniques. Due to its occurrence as microscopic grains, it requires analysis using a petrographic microscope, X-ray diffraction (XRD), or Raman spectroscopy. In meteorites, it forms characteristic, dark veins or aggregates resulting from shock metamorphism. ## Distinguishing from Similar Minerals It is distinguished from other olivine polymorphs, such as wadsleyite, by its crystallographic structure and Raman spectrum characteristics. As an inclusion in diamond, it can be confused with other deep mantle minerals, but its identity is confirmed solely by analytical methods. ## Crystal Forms Ringwoodite crystallizes in the isometric system. It usually occurs as anhedral (irregularly shaped) grains forming fine-grained aggregates. Its own, well-formed crystal shapes are rarely observed.

Geological environment

## Genesis Ringwoodite forms under conditions of extremely high pressure and temperature, corresponding to the Earth's mantle transition zone (depth from 520 to 660 km). It forms as a result of the phase transformation of wadsleyite, which in turn is a high-pressure variety of olivine. The second environment for its formation is shock metamorphic processes occurring during impacts of celestial bodies, which leads to its presence in some meteorites (chondrites). ## Mineral Associations In meteorites, ringwoodite co-occurs with other high-pressure minerals such as wadsleyite, akimotoite, as well as olivine, pyroxenes, kamacite, and taenite. As an inclusion in diamonds, it occurs alongside other deep-origin minerals, such as ferropericlase. ## Localities Confirmed occurrences of ringwoodite in meteorites include Tenham (Queensland, Australia), Peace River (Alberta, Canada), and Tissint (Morocco). As inclusions in diamonds, it has been identified in material from the Orapa mine (Botswana) and Juina (Brazil).

Rarity

Extremely rare

For collectors

## Quality Criteria The collector's value of ringwoodite is inextricably linked to the value of the specimen in which it occurs – most often a meteorite. It is not evaluated in terms typical for minerals (color, clarity, form) because it occurs as microscopic grains. The most valuable specimens are those (e.g., thin sections of meteorites) in which the presence of ringwoodite has been analytically confirmed and is visible under a microscope. Well-documented provenance and scientific history of the specimen increase its value. ## Popular Localities For collectors specializing in meteorites, specimens from classic localities such as the Tenham meteorite (Australia) or Peace River (Canada), from which this mineral was first described, are most sought after.

Care and storage

## Cleaning Due to its microscopic size and occurrence as inclusions or within a meteorite matrix, individual ringwoodite crystals are not subject to cleaning in the collector's sense. Meteorite specimens containing ringwoodite should be cleaned according to recommendations for the specific meteorite type, usually avoiding water and chemicals. ## What to Avoid Avoid any invasive cleaning methods, ultrasonics, and contact with chemicals. Meteorite specimens are sensitive to moisture, which can cause oxidation and disintegration. They should be protected from changes in temperature and humidity. ## Storage Meteorite fragments with ringwoodite should be stored under stable conditions, preferably in a dry environment, e.g., in sealed containers with a desiccant (silica gel). Display should be in closed showcases, away from direct sunlight and heat sources.

External references

Sources

Read more