Kushiroite

Chemical formula: CaAl(AlSi)O<sub>6</sub>

Kushiroite is a rare mineral from the pyroxene group, a calcium-aluminum clinopyroxene found mainly in meteorites.

## Characteristics Kushiroite is a mineral from the pyroxene group, belonging to the diopside-esseneite series. It is a calcium-aluminum clinopyroxene, closely related to esseneite and grossmanite. It forms very small, anhedral (lacking well-formed crystal faces) grains, usually less than 100 micrometers in size, occurring as inclusions in other minerals, such as anorthite. It is typically colorless and transparent. ## Physical Properties Due to the microscopic size of the crystals, most physical properties have not been fully investigated. The hardness is estimated at approximately 6 on the Mohs scale, and the density calculated from the formula and cell parameters is 3.41 g/cm³. The mineral is characterized by a vitreous luster. ## History and Name Kushiroite was named in honor of Ikuo Kushiro (born 1934), a Japanese petrologist and professor at the University of Tokyo, for his contributions to experimental petrology and research on magma genesis. The mineral was approved by the IMA in 2008, and its discovery was described in 2009. The type locality is the Allende meteorite, which fell in Mexico in 1969.

Properties

Mohs hardness
6
Luster
Vitreous
Streak
White
Density
3.41
Cleavage
Good on {110}
Transparency
Transparent
Crystal system
Monoclinic

Diagnostic features

## Identification Identification of kushiroite is possible only through advanced laboratory techniques, such as electron microprobe analysis (EMPA) for chemical composition and X-ray diffraction (XRD) for crystal structure determination. Visual identification is impossible due to the microscopic size of the grains and the lack of characteristic macroscopic features. ## Distinguishing from Similar Minerals Kushiroite is practically visually indistinguishable from other clinopyroxenes found in similar conditions, such as diopside, esseneite, davisite, or grossmanite. Differentiation requires precise chemical analysis, particularly the aluminum to silicon ratio. ## Crystal Forms Kushiroite occurs as anhedral, or irregular, grains, typically ranging from a few to several tens of micrometers in size. No well-formed crystals have been observed.

Geological environment

## Genesis Kushiroite is a mineral formed under high-temperature and low-pressure conditions. Its genesis is associated with condensation and crystallization processes in the early Solar System. It forms in calcium-aluminum-rich inclusions (CAIs) in carbonaceous chondrites. ## Mineral Associations This mineral coexists with other minerals typical of CAI inclusions in meteorites. It is most commonly associated with anorthite, melilite (åkermanite, gehlenite), spinel, diopside, grossmanite, davisite, and perovskite. ## Localities Kushiroite has been identified in several meteorites. The main confirmed localities are: - The Allende meteorite (CV3 carbonaceous chondrite), which fell in Chihuahua, Mexico – this is the type locality. - The Murchison meteorite (CM2 carbonaceous chondrite), found in Australia. - Other carbonaceous chondrites in which CAI inclusions of appropriate composition have been identified.

Rarity

Very rare

For collectors

## Quality Criteria Kushiroite does not occur as collectible specimens in the traditional sense. Its value is purely scientific. For research institutions and specialized meteorite collectors, the meteorite fragment itself (e.g., Allende), in which the presence of kushiroite has been analytically confirmed, is valuable. The mineralogical context and well-documented provenance of the specimen are important.

Care and storage

## Cleaning Due to its microscopic size and occurrence as inclusions in other minerals (mainly in meteorites), individual kushiroite specimens are not subject to cleaning. Any actions on the host rock should be carried out with the utmost care, preferably by a specialized laboratory. ## What to Avoid Avoid all chemicals, ultrasonics, and extreme temperature changes that could damage both the mineral itself and the surrounding rock matrix. ## Storage Meteorite specimens containing kushiroite should be stored under stable conditions, in a dry environment, away from direct sunlight and contaminants. It is best to use specialized containers for meteorite storage.

External references

Sources

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