Yafsoanite

Chemical formula: Ca₃Te₆+₂Zn₂+₃O₁₂

Jahnsite is a very rare calcium and zinc tellurate from the garnet group, prized for its intensely yellow, orange, or brown, well-formed crystals.

## Characteristics Jahnsite is a mineral belonging to the garnet supergroup, specifically to the tellurate garnet group. It forms very small, but usually well-formed, isometric crystals, most often in the form of a rhombic dodecahedron. These crystals rarely exceed 1 mm in diameter and occur as single individuals or small clusters within the host rock. The mineral is valued for its intense, vivid color. ## Physical Properties Jahnsite is characterized by a adamantine luster, which gives it a unique brilliance, especially on well-formed crystal faces. It is a relatively hard mineral, with a Mohs hardness of about 5.5. Due to the small size of the crystals, its density is difficult to measure, but the calculated value is approximately 6.36 g/cm³. It is transparent to translucent. ## Colors and Varieties This mineral occurs in various shades of yellow, from light yellow to golden yellow, as well as in orange, reddish-orange, and brown colors. No commercial or color varieties are distinguished. ## History and Name Jahnsite was first described in 1981 by L.A. Pertsev, I.V. Pskova, and N.V. Ekimenkova. Its name is an acronym derived from the Russian name of the Yakut Branch of the Siberian Department of the USSR Academy of Sciences (Yakutskii Filial Sibirskogo Otdeleniya Akademii Nauk SSSR - YaFSOAN SSSR), in recognition of the institution's contribution to geological research in the region.

Properties

Mohs hardness: 5.5
Luster: Adamantine
Streak: White
Density: 6.36
Cleavage: None
Fracture: Conchoidal
Transparency: Transparent to Translucent
Crystal system: Cubic

Diagnostic features

## Identification Identification of jahnsite is based on its characteristic, intense yellow or orange color, adamantine luster, and regular, isometric crystal form (rhombic dodecahedron). The locality of occurrence is also key – paragenesis with other rare tellurium minerals in skarns. ## Distinguishing from Similar Minerals Jahnsite can be confused with other garnets of similar coloration, such as spessartine or grossular, but differs from them by its significantly higher density and unique geological environment (occurrence with tellurides). Final confirmation requires advanced analytical methods, such as Raman spectroscopy or chemical analysis (EDS). ## Crystal Forms Jahnsite crystallizes in the isometric system, forming characteristic, well-formed crystals in the shape of a rhombic dodecahedron {110}. Crystals are usually very small, not exceeding 1 mm, and occur as single, dispersed grains or small aggregates.

Geological environment

## Genesis Jahnsite is a hydrothermal mineral, formed in contact zones, in magnesian skarns. It forms as a result of metasomatic processes occurring at high temperatures, associated with intrusions of igneous rocks into carbonate rocks (dolomites). ## Mineral Associations This mineral coexists with a wide range of other skarn and tellurium minerals. The most important include: calcite, dolomite, forsterite, fluorite, hydrotalcite, ludwigite, szaibelyite, as well as other rare tellurates and tellurides such as klyuchevskite, kuznetsovite, magnetite, and native tellurium. ## Localities The only confirmed and most important occurrence of jahnsite in the world is the Kuranakh gold deposit in Aldan, Yakutia (Sakha Republic) in Russia. This is its type locality.

Rarity

Extremely rare

For collectors

## Quality Criteria The most valuable jahnsite specimens are those that contain well-formed, sharp, and undamaged crystals with an intense, vivid color (golden yellow to orange). Crystals with an adamantine luster, clearly standing out from the host rock, are highly prized. Crystal size is a key factor – specimens with crystals approaching 1 mm are exceptionally desirable. The aesthetic composition with associated minerals is also important. ## Popular Localities The only source of collector specimens of jahnsite is its type locality – the Kuranakh deposit in Russia. All specimens available on the market come from this single location.

Care and storage

## Cleaning Due to the extreme rarity and small size of the crystals, jahnsite specimens usually do not require cleaning. If absolutely necessary, use only compressed air to remove dust. Avoid contact with water and any chemicals. ## What to Avoid Avoid ultrasonic cleaners, chemical agents, acids, bases, and sudden temperature changes. The crystals are fragile and small, so avoid any impacts or abrasions that could damage them or detach them from the matrix. ## Storage Specimens should be stored in stable conditions, in a dedicated collector's box, away from dust, moisture, and direct sunlight. It is best to store them in their original host rock to minimize the risk of damage.

Sources

IMA Mineral List (CNMNC)