Yoshiokaite

Chemical formula: Ca<sub>1-x</sub>(Al,Si)<sub>2</sub>O<sub>4</sub>

Yoshiokaite is an extremely rare tectosilicate mineral, discovered in lunar dust samples from the Apollo 15 mission.

## Characteristics Yoshiokaite is a microscopic mineral, occurring as small, tabular or platy crystals. Its maximum observed size does not exceed 150 micrometers. Due to its origin and size, it is a subject of scientific research rather than a collectible material in the traditional sense. It occurs as a component of lunar regolith. ## Physical Properties Yoshiokaite crystals are colorless and transparent, with a vitreous luster. Hardness and density have not been precisely measured due to the small size of the samples, but they are estimated based on the properties of its synthetic counterpart. ## Colors and Varieties This mineral is colorless. No varieties are distinguished. ## History and Name The name yoshiokaite was given in honor of Toshio Yoshioka (1917–1988), a Japanese mineralogist and professor at Okayama University, for his contributions to research on synthetic minerals. The mineral was approved by the International Mineralogical Association (IMA) in 1998, and its description was published in 2000. It was discovered in lunar regolith samples brought back by the Apollo 15 mission. ## Uses Yoshiokaite has no practical or commercial applications. Its significance is purely scientific, as an indicator of geological processes occurring on the Moon.

Properties

Mohs hardness
6.5
Luster
Vitreous
Streak
White
Density
2.7
Cleavage
Perfect on {0001}
Fracture
Uneven
Transparency
Transparent
Crystal system
Trigonal

Diagnostic features

## Identification Identification of yoshiokaite is possible only using advanced laboratory techniques, such as X-ray microdiffraction (XRD) and electron microprobe analysis (EMPA). Visual identification is not possible. ## Distinguishing from Similar Minerals In the lunar context, it can be confused with other colorless feldspar minerals, such as anorthite, with which it often co-occurs. Differentiation requires analysis of crystal structure and chemical composition. ## Crystal Forms Observed crystals are in the form of thin, hexagonal plates or flakes, often with irregular or rounded edges.

Geological environment

## Genesis Yoshiokaite forms under conditions of very high temperature and low pressure, characteristic of processes occurring on the lunar surface. Its presence is associated with impact melts or pyroclastic volcanic deposits. It is a high-temperature phase mineral in the CaAl₂O₄-SiO₂ system. ## Mineral Associations On the Moon, yoshiokaite co-occurs with anorthite, pyroxenes (pigeonite, augite), olivine, ilmenite, and silicate glass. ## Localities The only confirmed natural occurrence of yoshiokaite is the Moon. It was identified in regolith samples collected in the Hadley Rille region during the Apollo 15 mission.

Rarity

Extremely rare

For collectors

## Quality Criteria As an extraterrestrial mineral of microscopic size, yoshiokaite is not subject to standard collecting criteria. Its value is purely scientific. No specimens are in private collections and they are not available on the market. ## Popular Localities The only "locality" is the Apollo 15 landing site on the Moon.

Care and storage

## Cleaning Due to their microscopic size and unique origin, specimens containing yoshiokaite are not subject to standard cleaning procedures. They are stored under controlled laboratory conditions. ## What to Avoid Any manipulation, exposure to moisture, chemicals, or temperature changes that could damage or contaminate the sample should be avoided. ## Storage Lunar regolith samples containing yoshiokaite are stored in specialized laboratories (e.g., NASA Johnson Space Center) in a dry nitrogen atmosphere to prevent their degradation.

External references

Sources

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