Miyahisaite

Chemical formula: (Sr,Ca)₂Ba₃(PO₄)₃F

Miyahisaite is a very rare barium, strontium, and calcium phosphate, forming colorless, hexagonal crystals with a vitreous luster.

## Characteristics Miyahisaite is a mineral from the apatite group, characterized by a complex chemical composition including barium, strontium, and calcium. It occurs as small, hexagonal, prismatic crystals, which are typically colorless and transparent. Its crystals reach sizes up to 0.3 mm. It is a member of the apatite supergroup and belongs to the hedyphane group. ## Physical Properties This mineral has a hardness of 5 on the Mohs scale, which is typical for minerals of the apatite group. It has a vitreous luster and a white streak. The density calculated based on the formula and cell parameters is 4.75 g/cm³. The crystals are brittle and exhibit an uneven fracture. ## Colors and Varieties Miyahisaite is typically colorless. No colored varieties have been described. ## History and Name The mineral's name honors Professor Iwao Miyahisa (1927-1990), a specialist in ore deposit geology from Ehime University in Japan, for his contributions to the study of Besshi-type deposits. The mineral was approved by the International Mineralogical Association (IMA) in 2013 (IMA2013-073). It was described by Japanese mineralogists led by Daisuke Nishio-Hamane. ## Uses Due to its extreme rarity and microscopic crystal size, miyahisaite has no commercial or industrial applications. It is solely an object of scientific interest and a collector's item for specialized collectors of rare minerals.

Properties

Mohs hardness: 5
Luster: Vitreous
Streak: White
Density: 4.75
Cleavage: Indistinct
Fracture: Uneven
Transparency: Transparent
Crystal system: Hexagonal

Diagnostic features

## Identification Identification of miyahisaite is only possible using advanced analytical methods, such as energy-dispersive X-ray spectroscopy (EDS/EDX) to confirm its unique chemical composition (presence of barium, strontium, calcium, and phosphorus) and X-ray diffraction (XRD) to determine its crystal structure. Visually, it is indistinguishable from many other colorless, microscopic minerals. ## Differentiation from Similar Minerals Miyahisaite can be confused with other minerals from the apatite group, such as fluorapatite, hydroxylapatite, or other rare barium and strontium phosphates. Key to differentiation is precise determination of the chemical composition, especially the ratio of barium to strontium and calcium. ## Crystal Forms It forms hexagonal, prismatic crystals, terminated by pyramids. Crystals are elongated along the crystallographic c-axis.

Geological environment

## Genesis Miyahisaite forms in metamorphic rocks. It was discovered in manganese and iron deposits interbedded in a sequence of siliceous shales that underwent metamorphism under greenschist facies conditions. ## Mineral Associations At the type locality (Shobu mine), it is associated with celsian, quartz, cymrite, hematite, and braunite. ## Localities The only confirmed occurrence of miyahisaite in the world is its type locality: the Shobu mine in Ehime Prefecture on Shikoku Island, Japan.

Rarity

Extremely rare

For collectors

## Quality Criteria For collectors specializing in rare species and "micromount" specimens, the value of a miyahisaite specimen depends on the size and quality of crystal development, as well as the richness of its association with other minerals on the rock matrix. Well-formed, transparent crystals, clearly visible under a microscope, are the most desirable. ## Popular Localities The only source of specimens is the Shobu mine in Japan, which makes them extremely difficult to acquire on the collector's market.

Care and storage

## Cleaning Due to the microscopic size of the crystals, mechanical cleaning is not recommended and practically impossible without specialized equipment. If necessary, compressed air can be used to remove loose dust particles. ## What to Avoid Avoid contact with acids, which can damage phosphates. Specimens should not be subjected to ultrasonic cleaning or high temperatures. The crystals are brittle and susceptible to mechanical damage. ## Storage Miyahisaite specimens should be stored in specialized "micromount" boxes that protect them from dust, moisture, and physical damage. Avoid exposure to extreme temperature changes.

Sources

IMA Mineral List (CNMNC)