Zinkgruvanite

Chemical formula: Ba<sub>4</sub>Mn<sup>2+</sup><sub>4</sub>Fe<sup>3+</sup><sub>2</sub>(Si<sub>2</sub>O<sub>7</sub>)<sub>2</sub>(S<sup>6+</sup>O<sub>4</sub>)<sub>2</sub>O<sub>2</sub>(OH)<sub>2</sub>

Zinkgruvanite is a very rare, dark brown to black sorosilicate mineral, discovered in the Zinkgruvan mine in Sweden.

## Characteristics Zinkgruvanite is an extremely rare mineral that visually appears as very fine, lath-like or platy crystals, not exceeding 100 micrometers in length. It forms aggregates with a habit ranging from fan-shaped to spherulitic. Due to the microscopic size of the crystals, its macroscopic features are difficult to observe without specialized equipment. It occurs as dark brown to black, opaque masses. ## Physical Properties Zinkgruvanite crystals exhibit a luster ranging from submetallic to greasy. Hardness and density have not been precisely measured due to the very small size and rarity of the material. It is a brittle mineral. ## Colors and Varieties This mineral is dark brown to black, with a brownish streak. No varieties are known. ## History and Name Zinkgruvanite was first described in 2016 by Dan Holstam and collaborators. Its name comes from its discovery locality – the historic Zinkgruvan mine in the Askersund municipality, Sweden, which is also its type locality. It was approved by the International Mineralogical Association (IMA) under number 2015-111. ## Uses Zinkgruvanite, as an extremely rare mineral occurring only in microscopic quantities, has no practical applications. Its significance is purely scientific and as a collector's item, being a coveted object for specialized collectors of rare minerals.

Properties

Luster
Sub-metallic to greasy
Streak
Brownish
Cleavage
Perfect on {100}
Transparency
Opaque
Crystal system
Monoclinic

Diagnostic features

## Identification Identification of zinkgruvanite is impossible without advanced analytical techniques, such as Raman spectroscopy or chemical analysis using an electron microprobe (EDS/WDS). Preliminary indications may include its association with other rare minerals from the type locality (Zinkgruvan) and its dark color and submetallic luster. ## Distinguishing from Similar Minerals Macroscopically, it is indistinguishable from many other black, fine-grained oxide and silicate minerals. Definitive differentiation requires specialized laboratory analyses. ## Crystal Forms Zinkgruvanite forms very fine, elongated, lath-like crystals that combine into fan-shaped or spherical (spherulitic) aggregates.

Geological environment

## Genesis Zinkgruvanite forms as a result of metamorphic processes within iron, manganese, and zinc ore deposits. At its type locality (Zinkgruvan, Sweden), it occurs in skarns, which are metamorphic rocks formed at the contact of a magmatic intrusion with carbonate sedimentary rocks. ## Mineral Associations This mineral occurs in association with other rare minerals such as baryte, hedyphane, magnetite, filipstadite, manganoberyllite, eveite, and brandtite. It also co-occurs with more common minerals like calcite and quartz. ## Localities The only confirmed occurrence of zinkgruvanite in the world is its type locality – the Zinkgruvan mine, located near the town of the same name, in the Närke region of Sweden.

Rarity

Extremely rare

For collectors

## Quality Criteria As a microscopic mineral, the main criterion of value for a collector is the richness and quality of the aggregates visible under the microscope. The most desirable specimens are those with clearly formed, fan-shaped or spherulitic zinkgruvanite clusters, well-distinguished from the host rock. Association with other rare minerals from this locality is also important. ## Popular Localities The only source of specimens is the Zinkgruvan mine in Sweden. Collector material is extremely difficult to obtain and appears on the market very sporadically, usually from specialized rare mineral dealers.

Care and storage

## Cleaning Due to its extreme rarity and microscopic nature, zinkgruvanite specimens should not be cleaned by any mechanical or chemical means. It is best to leave them in their untouched state. ## What to Avoid Avoid any contact with chemicals, ultrasonics, as well as attempts at mechanical cleaning (e.g., with brushes), which could irreversibly damage the delicate crystals. The specimen should be protected from dust and vibrations. ## Storage Specimens should be stored exclusively in stable, sealed "micromount" boxes to protect them from physical damage and contamination. Display is only possible under a microscope.

Sources

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