Sakuraiite

Chemical formula: (Cu₁+,Cu₂+,Zn₂+,Fe₂+)₃(In₃+,Sn₄+)S₂-₄

Sakuraiite is a rare, metallic tin, indium, and copper mineral, found as microscopic grains in cassiterite-quartz veins.

## Characteristics Sakuraiite is a very rare mineral from the stannite group, chemically classified as a sulfide. It occurs as very fine, rounded or irregular grains, usually not exceeding 0.3 mm in size. Due to the microscopic size of its crystals, visual features are difficult to observe without specialized equipment. In reflected light under a polarizing microscope, it has a grayish-white color with a yellowish tint. ## Physical Properties As an opaque mineral, sakuraiite is characterized by a metallic luster. Its Mohs hardness is estimated at approximately 4, and its density, calculated based on chemical composition and unit cell parameters, is 4.51 g/cm³. It does not exhibit cleavage, and its fracture is uneven. ## History and Name The mineral was discovered in the Ikuno mine in Hyōgo Prefecture, Japan. Its description was published in 1965 by Akira Kato. The name honors the Japanese mineralogist and collector, Kin-ichi Sakurai (1912-1993), for his contributions to mineral research in Japan.

Properties

Mohs hardness: 4
Luster: Metallic
Streak: Black
Density: 4.51
Cleavage: None
Fracture: Uneven
Transparency: Opaque
Crystal system: Tetragonal

Diagnostic features

## Identification Identification of sakuraiite is impossible without advanced laboratory techniques. It requires chemical analysis (e.g., using an electron microprobe - EDS/WDS) and X-ray diffraction (XRD) studies to confirm the crystal structure. In reflected light under a microscope, it is very similar to kesterite and stannite. ## Distinguishing from similar minerals It can only be distinguished from kesterite, stannite, and czernickite, to which it is closely related, based on precise chemical composition analysis, which shows a high content of indium and tin. ## Crystal forms Sakuraiite forms exclusively microscopic, irregular or rounded grains, often intergrown with other minerals such as stannite or kesterite. No well-formed, idiomorphic crystals have been observed.

Geological environment

## Genesis Sakuraiite forms under hydrothermal conditions, in quartz-cassiterite veins. It forms as one of the later minerals in the crystallization sequence, often replacing earlier-formed stannite. ## Mineral associations This mineral co-occurs with cassiterite, stannite, kesterite, chalcopyrite, sphalerite, quartz, as well as rarer tin and indium minerals like roquesite and hocartite. ## Localities The only confirmed and thoroughly described occurrence of sakuraiite in the world is its type locality - the Ikuno mine, in Hyōgo Prefecture, Japan. This is a historic silver, copper, and tin mine, which is currently inactive and serves as a tourist attraction.

Rarity

Extremely rare

For collectors

## Quality criteria Sakuraiite specimens are not available on the collector's market in the traditional sense. Their value is purely scientific. Any analytically confirmed specimen, especially a polished section rich in this mineral, which allows for detailed studies of its optical and chemical properties, has research value. The most valuable samples come from the type locality.

Care and storage

## Cleaning Due to its extreme rarity and microscopic nature of occurrence, sakuraiite specimens are practically not subject to cleaning. Most often, these are polished sections intended for microscopic examination, which are cleaned exclusively with specialized optical preparations. ## What to avoid Contact with chemicals, especially acids, which can react with sulfides, should be avoided. Temperature and humidity changes are of little significance, as the mineral is usually embedded in epoxy resin (in polished sections) or protected by the surrounding host rock. ## Storage Microscopic specimens (polished sections) should be stored in specialized boxes, protecting the polished surface from scratches and dust. Host rocks containing sakuraiite should be stored under stable conditions, away from vibrations and chemical contamination.

Sources

IMA Mineral List (CNMNC)