Ishiharaite

Chemical formula: (Cu¹⁺,Ga³⁺,Fe³⁺,In³⁺,Zn²⁺)S²⁻

Ishiharaite is an extremely rare, black, metallic sulfide of copper, gallium, iron, indium, and zinc.

## Characteristics Ishiharaite is a mineral with a metallic luster and black color. It occurs as very fine, irregular grains, usually not exceeding 100 micrometers in size. Due to its size and mode of occurrence, individual crystals are not visible to the naked eye. It is observed in polished ore samples under a microscope as a component of mineral aggregates. ## Physical Properties This mineral is characterized by a metallic luster. It is opaque. Its Mohs hardness is estimated at 3.5, and its density, calculated based on the chemical formula and cell parameters, is 4.43 g/cm³. ## Colors and Varieties Ishiharaite has a uniform, black color. No color varieties or commercial forms are known. ## History and Name The mineral was discovered in the Toyoha mine in Hokkaido Prefecture, Japan. Its name, approved by the International Mineralogical Association (IMA) in 1983, honors Shunzo Ishihara (born 1934), a Japanese geologist and specialist in ore deposits, in recognition of his contributions to the study of tin and tungsten deposits in Southeast Asia.

Properties

Mohs hardness
3.5
Color
Dark gray
Luster
Metallic
Streak
Black
Density
4.43
Cleavage
None
Fracture
Uneven
Transparency
Opaque
Crystal system
Isometric

Diagnostic features

## Identification Identification of ishiharaite is possible only through advanced laboratory techniques, such as reflected light ore microscopy and chemical analysis using an electron microprobe (EDS/WDS). In reflected light, it has a grayish-white color with a slight brownish tint and is weakly anisotropic. ## Distinguishing from Similar Minerals Under the microscope, it can be confused with other fine-grained, gray sulfides, such as sphalerite, chalcopyrite, or tetrahedrite. Definitive differentiation requires chemical composition analysis, which reveals characteristic high contents of gallium and indium. ## Crystal Forms Ishiharaite forms exclusively anhedral (irregular) grains ranging from 10 to 100 micrometers in size, occurring as inclusions in other minerals, mainly sphalerite.

Geological environment

## Genesis Ishiharaite forms under hydrothermal conditions, in polymetallic tin-zinc-lead type veins. It is a product of crystallization from solutions rich in sulfur, copper, zinc, and rare metals such as gallium and indium. ## Mineral Associations This mineral occurs in close association with sphalerite (often as inclusions within it), chalcopyrite, pyrrhotite, cassiterite, arsenopyrite, as well as rarer tin minerals like stannite and kesterite. ## Localities The only confirmed occurrence of ishiharaite in the world is its type locality – the Toyoha mine, located in Sapporo, Hokkaido Prefecture on Hokkaido Island, Japan.

Rarity

Extremely rare

For collectors

## Quality Criteria From a collector's perspective, ishiharaite is not a mineral that forms aesthetic specimens. Its value is purely scientific and systematic. The only criterion is the confirmation of its presence in a research sample (e.g., in a polished section) from the type locality, which makes such material extremely valuable for specialized institutions and collectors of rare minerals (so-called "micromounts").

Care and storage

## Cleaning Due to its extreme rarity and microscopic grain size, ishiharaite specimens are not subject to cleaning under collector conditions. Any preparations (e.g., polished sections) require specialized laboratory equipment. ## What to Avoid Avoid all chemicals, ultrasonics, and mechanical abrasion, which could destroy the microscopic grains embedded in the rock matrix. ## Storage Specimens containing ishiharaite should be stored under stable conditions, away from moisture and chemical contaminants, preferably in specialized boxes or containers for research samples.

External references

Sources

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