Ammoniomagnesiovoltaite

Chemical formula: (N₃-H₄)₂Mg₅Fe₃+₃Al(S₆+O₄)₁₂·₁₈H₂O

Ammoniomagnesiovoltaite is a very rare sulfate from the voltaite group, distinguished by the presence of ammonium ions and magnesium in its complex chemical structure.

## Characteristics Ammoniomagnesiovoltaite is a member of the voltaite group, belonging to the sulfate class. This mineral forms very small, isometric (cubic) crystals, reaching up to 0.2 mm in size. It usually occurs as granular aggregates or as coatings and efflorescences on other minerals. Its presence is strictly linked to specific geochemical conditions, making it a mineralogical rarity. ## Physical Properties Ammoniomagnesiovoltaite crystals are characterized by a vitreous luster. Due to the small size of the crystals, many of its physical properties, such as hardness or density, have not been precisely determined. It is a brittle mineral. ## Colors and Varieties This mineral is dark green to almost black in color. No varieties have been distinguished. ## History and Name The mineral's name, approved by IMA in 2011 (IMA2011-031), refers to its chemical composition – the presence of ammonium (ammonio) and magnesium (magnesio) ions – and its structural relationship to voltaite, another mineral from this group. It was discovered on a burning coal mine dump of the "Marcel" mine in Radlin, Upper Silesia, Poland. ## Uses Ammoniomagnesiovoltaite has no industrial applications. Its significance is purely scientific and collectible, as a very rare and specific mineral species.

Properties

Luster: Vitreous
Streak: Green
Fracture: Conchoidal
Transparency: Translucent to opaque
Crystal system: Cubic

Diagnostic features

## Identification Mineral identification is primarily based on its specific occurrence (products of volcanic exhalations or coal dump fires), dark green color, and co-occurrence with other rare sulfates. Field identification is practically impossible and requires advanced analytical methods, such as Raman spectroscopy or X-ray diffraction (XRD). ## Distinguishing from similar minerals It can be confused with other minerals from the voltaite group, such as voltaite or ammoniovoltaite. Differentiation is only possible based on detailed chemical analysis (EDS/WDS) to confirm the presence and proportions of magnesium, iron, aluminum, and ammonium ions. ## Crystal forms It forms very small, well-formed, isometric crystals with a cubic habit. It also occurs as granular aggregates and coatings.

Geological environment

## Genesis Ammoniomagnesiovoltaite is a fumarolic (exhalative) mineral. It forms as a result of the reaction of hot volcanic gases or gases from burning coal dumps with surrounding rocks. It crystallizes in zones with temperatures ranging from 100 to 250°C in an environment rich in sulfur, ammonia, and metals. ## Mineral associations This mineral co-occurs with other sulfates formed under similar conditions, such as adranite, boussingaultite, godovikovite, mascagnine, tschermigite, as well as with salammoniac and native sulfur. ## Localities The only confirmed and described locality in the world (type locality) is the burning coal mine dump of the "Marcel" mine in Radlin, Upper Silesia, Poland.

Rarity

Extremely rare

For collectors

## Quality criteria As a "micromount" type mineral, its collector's value primarily depends on the presence of well-formed, sharp crystals, even if they are microscopic in size. Specimens with distinct, individual crystals on a contrasting matrix are most prized. Due to its extreme rarity, any correctly identified specimen is valuable to specialized collectors. ## Popular localities The only source of specimens is the type locality – the "Marcel" mine dump in Poland. Specimens from this location are extremely difficult to acquire and appear on the market very sporadically.

Care and storage

## Cleaning Specimens should only be cleaned with compressed air to remove dust. Any contact with water or other liquids is highly inadvisable, as the mineral is water-soluble. ## What to avoid Absolutely avoid contact with water, water vapor, and all chemicals. The mineral is sensitive to moisture and can dissolve or chemically degrade. Store away from heat sources and direct sunlight. ## Storage Ammoniomagnesiovoltaite specimens must be stored in sealed, dry containers, preferably with a desiccant (e.g., silica gel). The safest way to display it is in a closed display case with controlled humidity or in a specialized "micromount" box.

Sources

IMA Mineral List (CNMNC)