Shimazakiite

Chemical formula: Ca<sub>2</sub>B<sub>2</sub>O<sub>5</sub>

Shimazakiite is a rare calcium borate, forming colorless, tabular crystals with a vitreous luster, found in skarns.

## Characteristics Shimazakiite is a mineral from the borate group, chemically defined as calcium borate. It typically forms small, colorless, tabular or platy crystals, which can occur as radial or chaotic aggregates. Individual crystals rarely exceed 1 mm in length. Due to its composition and formation conditions, it is a scientifically interesting mineral. ## Physical Properties The mineral is characterized by a hardness of 5 on the Mohs scale. It has a vitreous luster and is transparent. The density of shimazakiite has been calculated as 2.72 g/cm³. It does not exhibit fluorescence under ultraviolet light. ## Colors and Varieties Shimazakiite is colorless. No colored varieties or trade names are known. ## History and Name The mineral was named after Professor Hidehiko Shimazaki (born 1939), a Japanese mineralogist and economic geologist from the University of Tokyo, in recognition of his contributions to research on skarn deposits in Japan. It was approved by the International Mineralogical Association (IMA) in 2005, and its discovery was first described in 2006. ## Uses Shimazakiite has no industrial applications. It is solely an object of interest for collectors specializing in rare minerals and a subject of scientific research.

Properties

Mohs hardness
5
Luster
Vitreous
Streak
White
Density
2.72
Cleavage
Good on {100}
Fracture
Uneven
Transparency
Transparent
Crystal system
Monoclinic

Diagnostic features

## Identification Shimazakiite is difficult to identify visually without specialized equipment. It is recognized by its crystal habit – small, colorless, tabular or platy – and its characteristic occurrence environment (skarns). Final identification requires advanced analytical methods, such as X-ray diffraction (XRD) or chemical analysis. ## Distinguishing from Similar Minerals It can be confused with other colorless minerals found in skarns, such as quartz, calcite, or some zeolites. It differs from quartz by its lower hardness, and from calcite by its lack of reaction with hydrochloric acid. Unlike many zeolites, it forms more defined, tabular crystals. ## Crystal Forms Crystals are tabular or platy, often elongated. They occur as single, disseminated crystals or form radial and irregular aggregates on the surface of the host rock.

Geological environment

## Genesis Shimazakiite is a mineral of metamorphic origin. It forms as a result of contact processes in calc-silicate skarns, which develop at the contact zone between granitoid intrusions and limestones or dolomites. It is a product of the late stages of skarn formation. ## Mineral Associations This mineral co-occurs with other minerals typical of skarns, such as calcite, wollastonite, garnets (andradite, grossular), diopside, vesuvianite, datolite, and other borates, e.g., olshanskyite. ## Localities The most important and also the type locality of shimazakiite is the Fuka mine in Okayama Prefecture, Japan. This is the only confirmed and well-documented location of this mineral worldwide.

Rarity

Very rare

For collectors

## Quality Criteria The collector appeal of shimazakiite primarily depends on the richness and aesthetics of the crystal aggregates on the rock matrix. Specimens with well-formed, transparent, abundant crystals forming radial groups are most valued. The size of individual crystals, although usually small, also affects the value of the specimen. ## Popular Localities The only source of collector specimens is the Fuka mine in Japan. Material from this locality is extremely rare on the market and sought after by collectors specializing in systematic minerals and rare species.

Care and storage

## Cleaning Specimens should only be cleaned with compressed air to remove dust. Due to the rarity and delicacy of the crystals, contact with water and any chemical agents should be avoided. ## What to Avoid Avoid ultrasonic cleaners, steam cleaning, and contact with acids and other chemicals that can damage the delicate crystals. The mineral is susceptible to mechanical damage. ## Storage It is recommended to store specimens in closed, stable containers (micromount type) to protect them from dust, moisture, and mechanical damage. Avoid exposure to sudden temperature changes.

Sources

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