Zagamiite

Chemical formula: CaAl₂Si₃.₅O₁₁

Zagamiite is an extremely rare mineral from the axinite group, discovered in the Zagami meteorite, known only from microscopic grains.

## Characteristics Zagamiite is a mineral from the axinite group, approved by the IMA in 2017. It occurs as extremely small, anhedral (lacking its own crystallographic form) grains not exceeding 15 micrometers in size. These grains are embedded in maskelynite – glass formed as a result of shock-induced transformation of plagioclase. Due to its microscopic size and occurrence as inclusions, the visual characteristics of a typical specimen cannot be described on a macroscopic scale. ## Physical properties Due to the extremely small size of the grains, most physical properties of zagamiite have not been determined. Hardness, density, luster, and fracture remain unknown. It is transparent to translucent. ## Colors and varieties The observed grains are colorless. No varieties of this mineral have been distinguished. ## History and name The mineral's name comes from the Zagami meteorite, in which it was discovered. This meteorite fell in 1962 near the town of Zagami in Nigeria. Zagamiite was described by Chi Ma, Oliver Tschauner, and John R. Beckett and officially recognized as a new mineral in 2017 (IMA2017-012). It is a high-pressure polymorph of calcite. ## Uses Zagamiite has no practical or commercial applications. Its significance is purely scientific, serving as an indicator of high-pressure and high-temperature conditions prevalent during impacts in space.

Properties

Color
colorless
Streak
White
Density
3.79
Transparency
Transparent
Crystal system
Hexagonal

Diagnostic features

## Identification Identification of zagamiite is possible only through advanced laboratory techniques, such as electron microprobe analysis (EMPA) and electron backscatter diffraction (EBSD). It is not possible to identify it on a macroscopic scale or even with a standard petrographic microscope. ## Distinguishing from similar minerals Zagamiite is embedded in maskelynite (shock-transformed plagioclase) and co-occurs with other high-pressure phases. Distinguishing it from the surrounding matrix and other microminerals requires specialized analysis of chemical composition and crystal structure. ## Crystal forms This mineral forms only very fine, anhedral (irregular) grains.

Geological environment

## Genesis Zagamiite is a shock mineral, formed under extremely high-pressure (estimated at 20-23 GPa) and high-temperature (approximately 2000-2500 °C) conditions. Such conditions arise during celestial body collisions. In the case of the Zagami meteorite, this mineral crystallized from an impact melt in shock veins cutting through the rock. ## Mineral associations Zagamiite occurs in paragenesis with other shock minerals and components of the Zagami meteorite. It co-occurs with maskelynite (in which it is embedded), ringwoodite, akimotoite, stishovite, as well as minerals from the pyroxene and olivine groups. ## Localities The only confirmed locality of zagamiite in the world is the Zagami meteorite – a shergottite (Martian meteorite) that fell in Nigeria.

Rarity

Extremely rare

For collectors

## Quality criteria Zagamiite is not an item of collector's trade as a separate mineral. The collector's value lies in fragments of the Zagami meteorite itself. The presence of microscopically confirmed, rare mineral phases, such as zagamiite, enhances the scientific and potentially market value of a given meteorite fragment, especially for specialized research institutions and collectors of extraterrestrial materials. ## Popular localities The only source is the Zagami meteorite, fragments of which are found in institutional and private collections worldwide.

Care and storage

## Cleaning Not applicable. The mineral occurs exclusively as microscopic inclusions within the meteorite structure and is neither isolated nor cleaned. ## What to avoid Not applicable. Zagami meteorite specimens containing zagamiite should be protected from moisture, chemicals, and mechanical damage, like any valuable meteoritic material. ## Storage Fragments of the Zagami meteorite should be stored under stable conditions, preferably in a dry environment, in specialized containers protecting against contamination and moisture.

External references

Sources

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