Boussingaultite
Chemical formula: (N<sup>3-</sup>H<sub>4</sub>)<sub>2</sub>Mg(S<sup>6+</sup>O<sub>4</sub>)<sub>2</sub>·6H<sub>2</sub>O
Boussingaultite is a hydrated magnesium ammonium sulfate, occurring as brittle, colorless or white crystals and efflorescences.
Properties
- Mohs hardness
- 2.5
- Luster
- Vitreous
- Streak
- White
- Density
- 1.703
- Cleavage
- Good on {010}
- Fracture
- Conchoidal
- Transparency
- Transparent to Translucent
- Crystal system
- Monoclinic
Diagnostic features
## Identification A key diagnostic feature of boussingaultite is its water solubility. The mineral is very soft (hardness 2.5), light, and has a characteristic vitreous luster. It often occurs as efflorescences and coatings in specific environments, such as volcanic fumaroles. ## Distinguishing from Similar Minerals Boussingaultite can be confused with other water-soluble sulfates, such as epsomite (Epsom salt) or picromerite. Epsomite crystallizes in the orthorhombic system and often forms acicular crystals. Picromerite has a very similar chemical composition and properties, and distinguishing them without advanced studies (e.g., X-ray diffraction) is practically impossible. Boussingaultite differs from gypsum by its significantly lower hardness and water solubility. ## Crystal Forms It crystallizes in the monoclinic system. Well-formed crystals are rare and usually appear as short prisms or tablets. Most often, it forms fibrous aggregates, crusty coatings, and granular aggregates.
Geological environment
## Genesis Boussingaultite is a mineral of volcanic or geothermal origin. It forms as a result of sublimation from hot gases (fumaroles) at temperatures ranging from 70 to 130°C. It can also form as an evaporation product in some salt lakes or as a product of coal mine dump fires. ## Mineral Associations It occurs in association with other fumarolic minerals, such as native sulfur, sassolite, mascagnite, and also with sulfates such as epsomite, picromerite, and mohrite. ## Localities The most important boussingaultite localities in the world are the Larderello geothermal fields in Tuscany (Italy), where it was discovered. It is also found in volcanic areas, e.g., on Mount Vesuvius (Italy), Mutnovsky Volcano in Kamchatka (Russia), and in The Geysers in California (USA). It also occurs as a product of coal fires, e.g., in Pennsylvania (USA).
Rarity
Rare
For collectors
## Quality Criteria The most prized specimens by collectors are those with well-formed, transparent crystals, which are very rare. Rich efflorescences and fibrous aggregates on original matrix rock are also attractive. Due to the mineral's instability, it is crucial that the specimen is well-preserved and shows no signs of dissolution or recrystallization. ## Popular Localities Classic and most sought-after specimens come from the type locality - Larderello in Italy. Material from the fumaroles of Mount Vesuvius and from geothermal fields in California is also valued in specialized collections.
Care and storage
## Cleaning Boussingaultite is water-soluble, so it must absolutely not be cleaned wet. Only a soft brush or compressed air from a safe distance should be used to remove dust. ## What to Avoid Avoid contact with water and any liquids that could dissolve it. The mineral is sensitive to atmospheric moisture, which can lead to its slow degradation. It should be protected from high temperatures and direct sunlight. ## Storage Boussingaultite specimens require storage in dry conditions. It is best to place them in a sealed, airtight container (e.g., a "membrane box" type) or in a display cabinet with a moisture absorber (e.g., silica gel).