Magnesioalterite

Chemical formula: Mg<sub>2</sub>Fe<sup>3+</sup><sub>4</sub>(S<sup>6+</sup>O<sub>4</sub>)<sub>4</sub>((C<sub>2</sub>)<sup>6+</sup>O<sub>4</sub>)<sub>2</sub>(OH)<sub>4</sub>·17H<sub>2</sub>O

Magnesioalterite is an extremely rare magnesium and iron sulfate and oxalate, forming microscopic, yellow crystals.

## Characteristics Magnesioalterite is a hydrated magnesium and iron sulfate and oxalate. It forms very small, prismatic crystals that rarely exceed 0.2 mm in length. Most often, it occurs as radial or divergent aggregates of an intensely yellow color. It is a transparent mineral with a vitreous luster. ## Physical Properties The mineral's luster is vitreous. It is transparent. The calculated density is 2.21 g/cm³. Hardness has not been determined. Due to its chemical composition and hydration, it is likely brittle and sensitive to changes in humidity and temperature. ## Colors and Varieties This mineral occurs exclusively in one color – yellow. No color varieties or commercial names are known. ## History and Name The name magnesioalterite refers to its chemical composition – the dominant magnesium (magnesio) and its relationship to the structurally similar mineral, alterite. It was officially approved by the International Mineralogical Association (IMA) in 2020. It was first described by Anthony R. Kampf and his team in 2022. The type locality is the Alcaparrosa mine in Chile. ## Uses Due to its extreme rarity and microscopic crystal sizes, magnesioalterite has no industrial applications. It is solely an object of scientific research and is valued by specialized collectors of rare minerals.

Properties

Luster
Vitreous
Streak
Light yellow
Density
2.21
Transparency
Transparent
Crystal system
Monoclinic

Diagnostic features

## Identification Identification of magnesioalterite in the field is practically impossible. Indicative features may include: yellow color, vitreous luster, and occurrence in the form of small, radial aggregates. Definitive identification requires advanced analytical methods, such as X-ray diffraction (XRD) or X-ray microanalysis (EDS/WDS), which can confirm its unique chemical composition. ## Distinguishing from Similar Minerals It can be confused with other yellow secondary sulfates that often co-occur in the same environment, such as copiapite, metavoltine, or rhomboclase. Differentiation from these is based on chemical analysis, which shows the presence of both magnesium and the oxalate group, which is unique to magnesioalterite and alterite. ## Crystal Forms It forms elongated, prismatic crystals, usually no longer than 0.2 mm. These crystals arrange themselves into characteristic, divergent or radial aggregates.

Geological environment

## Genesis Magnesioalterite is a secondary mineral, formed in post-mining conditions. It forms in the oxidation zone of sulfide deposits in an arid climate. Its genesis is related to the reaction of acidic mine waters, rich in sulfates, with bird droppings (guano), which are a source of oxalic acid. ## Mineral Associations It co-occurs with other rare sulfates and oxalates, such as alterite, coquimbite, copiapite, halotrichite, tamarugite, voltaite, metavoltine, and rhomboclase. ## Localities The only confirmed locality of magnesioalterite in the world is the Alcaparrosa mine, located near the town of Calama in the El Loa Province, Antofagasta Region, Chile.

Rarity

Extremely rare

For collectors

## Quality Criteria Due to the extreme rarity of the mineral, every specimen is considered valuable. The most highly prized samples are those with rich, well-formed crystalline aggregates on a small rock matrix. An aesthetic association with other rare, color-contrasting minerals is an additional advantage. ## Market Prices There is no established market for this mineral. Specimens appear on the market extremely rarely and mainly go to institutional collections and highly specialized collectors of rare minerals. Prices are determined individually and can be very high. ## Popular Localities All known specimens come from a single location – the Alcaparrosa mine in Chile, which is its type locality.

Care and storage

## Cleaning Magnesioalterite specimens are extremely delicate and likely water-soluble. They should not be wet cleaned. To remove dust, a gentle stream of compressed air or a very soft brush can be used, proceeding with the utmost care. ## What to Avoid Contact with water, acids, and other chemicals must be strictly avoided. As a hydrated mineral, it is sensitive to high temperatures, which can cause dehydration and destruction. It should be protected from direct sunlight and sudden changes in humidity. ## Storage It is recommended to store specimens in stable, dry conditions. Ideally, they should be placed in a sealed, lidded "perky box" to protect them from dust, mechanical damage, and fluctuations in ambient humidity.

Sources

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