Hinokageite

Chemical formula: Mn<sup>2+</sup>Mg(SiO<sub>4</sub>)

Hinokageite is a very rare, newly discovered mineral from the olivine group, being a manganese-magnesium silicate.

## Characteristics Hinokageite is an extremely rare mineral belonging to the olivine group. It was approved as a new mineral species by the IMA in 2023. It occurs as very small, anhedral (lacking crystal faces) grains, usually less than 100 micrometers in size, intergrown with other minerals. Its identification requires advanced analytical techniques. ## Physical Properties Due to the microscopic size of the grains, most physical properties, such as hardness, density, luster, or transparency, have not yet been determined on macroscopic material. The hardness is estimated to be around 6 on the Mohs scale, and the density calculated based on the formula and cell parameters is 3.82 g/cm³. ## Colors and Varieties Observed hinokageite grains are pale yellow. In transmitted light, it is colorless and does not exhibit pleochroism. No varieties of this mineral have been distinguished. ## History and Name The mineral's name comes from its discovery locality – Hinokage Town in Miyazaki Prefecture, Japan. It was discovered by a Japanese team of mineralogists, and its description was published in 2024. It is the manganese analog of forsterite and the magnesium analog of tephroite.

Properties

Mohs hardness
6
Luster
Vitreous
Streak
White
Density
3.82
Cleavage
Good on {010}, imperfect on {100}
Transparency
Transparent
Crystal system
Orthorhombic

Diagnostic features

## Identification Identification of hinokageite is impossible without advanced laboratory methods. It requires chemical analysis (electron microprobe, EDS) to determine its composition (dominance of Mn and Mg) and X-ray diffraction (XRD) or electron diffraction to confirm its olivine-group crystal structure. Visually, it is indistinguishable from other olivines occurring in similar parageneses. ## Distinguishing from Similar Minerals It can be confused with other minerals from the olivine group, such as forsterite (Mg₂SiO₄), tephroite (Mn₂SiO₄), or olivine (Mg,Fe)₂SiO₄. Differentiation is possible only based on precise chemical analysis, which for hinokageite must show a Mn to Mg ratio close to 1:1. ## Crystal Forms To date, it has only been observed as very small, irregular, anhedral grains intergrown in the rock.

Geological environment

## Genesis Hinokageite forms as a result of high-grade contact metamorphism (skarns in the sanidinite facies). It forms in manganese-rich rocks that have been subjected to very high temperatures (over 800°C) and low pressure, in contact with igneous intrusions. ## Mineral Associations At its type locality (Hinokage, Japan), it coexists with minerals such as tephroite, welshite, alabandite, galaxite, pyroxmangite, sonolite, as well as various manganese-rich amphiboles and pyroxenes. ## Localities The only confirmed occurrence of hinokageite in the world is its type locality: Hinokage Town, Miyazaki Prefecture, Kyushu Island, Japan.

Rarity

Extremely rare

For collectors

## Quality Criteria As a microscopic mineral, the collector's value of a hinokageite specimen is not based on traditional aesthetic criteria. The most important factor is the certainty of identification, confirmed by a reputable laboratory. The value is enhanced by the richness of the mineral association on the specimen and the quantity and "readability" of hinokageite grains in the rock matrix, visible under a microscope. ## Popular Localities The only source of material is the type locality in Japan. Specimens are extremely difficult to obtain and primarily go to scientific institutions and highly specialized collections of rare or systematic minerals.

Care and storage

## Cleaning Due to the extreme rarity and microscopic size of grains intergrown in the host rock, hinokageite specimens are not subject to cleaning in the traditional sense. Any attempts at mechanical or chemical intervention may destroy the unique material. ## What to Avoid Avoid all chemicals, ultrasonics, temperature changes, and attempts to isolate grains from the rock matrix. The specimen should be protected from abrasion and mechanical damage. ## Storage Specimens containing hinokageite, whether research material or a unique collector's acquisition, should be stored under stable conditions, in a specialized "micromount" box, protecting them from dust, moisture, and physical damage.

Sources

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