Erssonite

Chemical formula: CaMg<sub>7</sub>Fe<sup>3+</sup><sub>2</sub>(OH)<sub>18</sub>(S<sup>6+</sup>O<sub>4</sub>)<sub>2</sub>·12H<sub>2</sub>O

Erssonite is an extremely rare, hydrated calcium, magnesium, and iron sulfate, forming microscopic, hexagonal, yellow crystals.

## Characteristics Erssonite is a sulfate mineral, described in 2021. It occurs as extremely small, hexagonal, tabular crystals, rarely exceeding 20 micrometers in diameter and 5 micrometers in thickness. These crystals form rosette-like or spherical aggregates. Due to their microscopic size, visual features are only visible under high magnification. ## Physical Properties Due to the microscopic size of the crystals, most physical properties, such as hardness, luster, or transparency, have not been determined. The density was calculated based on the formula and unit cell parameters and is 2.13 g/cm³. ## Colors and Varieties This mineral has a characteristic yellow color. No varieties have been distinguished. ## History and Name The mineral's name honors Swedish mineral collector, Andreas Ersson (born 1971), for his contributions to the mineralogy of the Långban quarry in Sweden. Erssonite was approved by the International Mineralogical Association (IMA) in 2020 (IMA2020-040), and its description was published in 2021. ## Applications Erssonite has no industrial applications. Its significance is purely scientific and as a collector's item, as a unique and newly discovered mineral.

Properties

Luster
Vitreous
Streak
Light yellow
Density
2.13
Cleavage
Perfect on {0001}
Transparency
Transparent
Crystal system
Hexagonal

Diagnostic features

## Identification Identification of erssonite is impossible without advanced laboratory techniques, such as scanning electron microscopy (SEM) combined with chemical analysis (EDS) and X-ray diffraction (XRD). In collector's conditions, identification relies on trust in a label from a reputable source. ## Distinguishing from Similar Minerals Erssonite can be confused with other secondary, microcrystalline sulfates occurring in similar environments. Certain distinction requires specialized analysis of chemical composition and crystal structure. ## Crystal Forms It forms microscopic, hexagonal, tabular crystals, often grouped into rosette-like or spherical aggregates.

Geological environment

## Genesis Erssonite is a secondary mineral, formed by hydrothermal processes in altered skarns. In its type locality (Långban), it formed in voids within dolomite. ## Mineral Associations This mineral co-occurs with minerals such as dolomite, calcite, magnesite, baryte, hematite, and serpentine group minerals. ## Localities The only confirmed occurrence of erssonite in the world is its type locality: the Långban quarry in Filipstad Municipality, Värmland County, Sweden.

Rarity

Extremely rare

For collectors

## Quality Criteria Due to the microscopic nature of the mineral, the main criterion for value is the richness and quality of the aggregates visible under the microscope. Specimens where erssonite forms distinct, well-formed rosettes on a contrasting matrix are most highly prized. The certainty of identification from the type locality is also crucial. ## Popular Localities The only source of specimens is the Långban quarry in Sweden, which is known for the occurrence of many rare and unique minerals.

Care and storage

## Cleaning Erssonite specimens, due to their extreme fragility and microscopic size, should not be cleaned mechanically or chemically. Any attempt at cleaning risks irreversible destruction of the mineral. ## What to Avoid Avoid contact with water, chemicals, as well as any vibrations and shocks. As a hydrated mineral, it is sensitive to changes in temperature and humidity, which can lead to its dehydration and disintegration. It should be protected from direct sunlight. ## Storage Specimens should be stored exclusively in stable conditions, in closed, padded "micromount" containers, to minimize the risk of mechanical damage and the effects of atmospheric changes.

Sources

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