Goldschmidtite

Chemical formula: KNb<sup>5+</sup>O<sub>3</sub>

Goldschmidtite is an extremely rare perovskite-group mineral, a potassium niobate found as a single inclusion in a diamond.

## Characteristics Goldschmidtite is a microscopic mineral, identified as a single, dark green to black, opaque grain approximately 100 micrometers in size, trapped within a diamond. Due to its unique origin and extreme rarity, its full visual characterization is limited to microscopic observations. This mineral belongs to the perovskite structural group. ## Physical Properties As a mineral from the perovskite group, it can be assumed that its hardness is approximately 5.5 on the Mohs scale, and its density is relatively high, estimated at 4.77 g/cm³. The luster is described as submetallic. However, these properties are largely extrapolated based on crystallographic data and chemical composition, rather than direct measurements on a larger sample. ## History and Name The mineral's name honors Victor Moritz Goldschmidt (1888–1947), a Norwegian mineralogist and geochemist, recognized as one of the fathers of modern geochemistry and crystal chemistry. The mineral was officially approved by the IMA in 2018 (IMA 2018-034), and its discovery was published in 2019. It was identified in a diamond originating from the Koffiefontein mine in the Republic of South Africa.

Properties

Mohs hardness
5.5
Luster
Sub-Metallic
Streak
Dark brown
Density
4.77
Transparency
Opaque
Crystal system
Cubic

Diagnostic features

## Identification Identification of goldschmidtite is possible only through advanced analytical techniques, such as Raman spectroscopy, single-crystal X-ray diffraction, and electron microprobe. Visual identification is impossible due to its microscopic size and occurrence as an inclusion. Key is the determination of its chemical composition (potassium niobate) and perovskite crystal structure. ## Distinguishing from Similar Minerals Other dark, opaque inclusions in diamonds, such as chromite, ilmenite, pyrope, or sulfides, may appear similar under a microscope. Differentiation requires chemical analysis. The presence of niobium and potassium in a perovskite structure is a characteristic unequivocally indicating goldschmidtite. ## Crystal Forms The mineral was found as a single, anhedral (not exhibiting external crystallographic forms) grain. Theoretically, crystallizing in the isometric system, it could form cubic or octahedral crystals, but this has not been observed in nature.

Geological environment

## Genesis Goldschmidtite formed under conditions of extremely high pressure and temperature prevailing in the Earth's upper mantle, at a depth of approximately 170 km. Its chemical composition, rich in potassium and niobium, indicates metasomatic enrichment of a mantle fragment from which the diamond crystallized. This process involves the infiltration of mantle rocks by fluids or melts rich in incompatible elements such as K, Nb, La, and Ce. ## Mineral Associations This mineral occurs as an inclusion in diamond. In the same diamond, olivine inclusions were also identified, which is typical for diamonds from a peridotitic source in the Earth's mantle. ## Localities The only confirmed locality in the world is the Koffiefontein diamond mine in the Free State province of the Republic of South Africa. The mineral was found in a single diamond from this location.

Rarity

Extremely rare

For collectors

## Quality Criteria As there is only one known microscopic specimen, traditional quality criteria do not apply. The scientific value of this mineral is inestimable. Any future specimen, regardless of size, would be extremely valuable for science and collecting. Key would be the confirmation of its identity and documentation of its association with diamond. ## Popular Localities The only known locality is the Koffiefontein mine in South Africa. This is not a locality accessible to collectors, and finding another specimen is extremely unlikely.

Care and storage

## Cleaning Due to its occurrence exclusively as a microscopic inclusion in diamond, cleaning the mineral itself is not possible. The diamond specimen in which it is found can be cleaned using standard methods for diamonds, e.g., ultrasonics or steam, however, any intervention should be carried out with the utmost care by specialists to avoid damaging the unique inclusion. ## What to Avoid Any invasive techniques that could compromise the structure of the host diamond should be avoided. Heating to extreme temperatures or using aggressive chemicals is inadvisable. Protection against mechanical damage is crucial. ## Storage The only known specimen is stored under laboratory conditions, ensuring protection against shocks, temperature changes, and theft. Any potential future specimen should be treated as a scientific unique item and stored in a similarly secured environment.

Sources

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