Kollerite

Chemical formula: (N<sup>3-</sup>H<sub>4</sub>)<sub>2</sub>Fe<sup>3+</sup>(S<sup>4+</sup>O<sub>3</sub>)<sub>2</sub>(OH)·H<sub>2</sub>O

Kollerite is an extremely rare iron and ammonium sulfite, forming microscopic, yellow crystals in coal mine fire environments.

## Characteristics Kollerite is a hydrated iron (III) and ammonium sulfite. It occurs as extremely small, acicular or bladed crystals, rarely exceeding 0.1 mm in length. It forms radial aggregates or occurs as single, scattered crystals on the substrate. Due to its microscopic size, its visual features are difficult to observe without magnification. ## Physical properties The crystals are too small to reliably determine their hardness, density, or optical properties macroscopically. The luster is described as vitreous. It is transparent to translucent. ## Colors and varieties This mineral has a characteristic bright yellow color. No varieties are known. ## History and name Kollerite was approved as a new mineral by the IMA in 2023 (IMA2023-090). The name honors Norbert Koller (born 1958), an Austrian mineral collector who found the first samples of this mineral. It was discovered on the dump of a former lignite mine in Köflach, Styria, Austria. ## Uses Kollerite has no industrial application. It is solely an object of scientific and collecting interest for specialized micromineral collectors.

Properties

Luster
Vitreous
Streak
White
Cleavage
Perfect on {010}
Transparency
Transparent to translucent
Crystal system
Monoclinic

Diagnostic features

## Identification Practical identification of kollerite requires specialized analytical equipment (e.g., Raman spectroscopy, EDS) due to its microscopic size and occurrence in complex parageneses. A visual feature is its bright yellow color and acicular habit of crystals in radial aggregates, but this is not sufficient for certain identification. ## Distinguishing from similar minerals It can be confused with other secondary sulfates and sulfites formed in coal mine fire zones, such as adranite or godovikovite. Distinguishing it from these is almost exclusively possible using advanced analytical methods. ## Crystal forms It forms very fine, acicular or bladed crystals, usually gathered in radial or stellate aggregates. Single crystals are rare.

Geological environment

## Genesis Kollerite is a secondary mineral of anthropogenic origin. It forms as a result of reactions of gases (mainly ammonia and sulfur dioxide) escaping from underground fire zones in coal mines. It crystallizes directly from the gas phase (sublimation) on cooler rock surfaces on mine dumps. ## Mineral associations At the type locality (Köflach, Austria), it co-occurs with adranite, sal ammoniac, native sulfur, millosevichite, tschermigite, and godovikovite. ## Localities The only confirmed locality in the world is the dump of the former lignite mine in Köflach, Styria, Austria.

Rarity

Extremely rare

For collectors

## Quality criteria The quality of a specimen depends on the richness and aesthetics of the microscopic aggregates. The most valued samples are those with well-formed, radial clusters of bright yellow crystals, clearly visible on a contrasting substrate. The size of the aggregates and their abundance on the rock matrix are key factors. ## Popular localities The only source of specimens is the type locality in Köflach, Austria. All samples available on the collector's market come from this single location.

Care and storage

## Cleaning Specimens should be handled with the utmost care. Due to its water solubility and extreme delicacy, mechanical cleaning or cleaning with liquids is impossible and will destroy the mineral. Specimens should be protected from dust. ## What to avoid Contact with water, water vapor, and high humidity, which can dissolve or damage the crystals, must be absolutely avoided. Avoid all chemicals, ultrasound, and temperature changes. The mineral is very sensitive to environmental changes. ## Storage Store only in tightly sealed "perky box" type containers or similar, preferably with a desiccant (e.g., silica gel). Protect from shocks, vibrations, and direct sunlight.

Sources

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