Bararite
Chemical formula: (N<sup>3-</sup>H<sub>4</sub>)<sub>2</sub>SiF<sub>6</sub>
Bararite is a rare mineral from the halide group, being a low-temperature, trigonal polymorph of ammonium hexafluorosilicate.
Properties
- Mohs hardness
- 2.5
- Luster
- Vitreous
- Streak
- White
- Density
- 2.153
- Cleavage
- None
- Fracture
- Conchoidal
- Transparency
- Transparent to Translucent
- Crystal system
- Trigonal
Diagnostic features
## Identification A key diagnostic feature of bararite is its reaction to moisture – it is water-soluble. It forms characteristic white or colorless, earthy coatings in specific environments, such as burning coal mine dumps. Low hardness and density are also helpful in identification. ## Distinguishing from Similar Minerals Bararite can be confused with other water-soluble sulfates or halides, such as sal ammoniac (ammonium chloride) or mascagnite (ammonium sulfate), which occur in similar environments. It is distinguished from sal ammoniac by the lack of a salty taste. Certain differentiation from cryptohalite, its dimorphic variety, requires advanced analytical methods, such as X-ray diffraction (XRD). ## Crystal Forms Bararite most often occurs as very fine, hexagonal or trigonal crystals, which form crusty, powdery, or earthy coatings and aggregates. Well-formed, single crystals visible to the naked eye are rarely observed.
Geological environment
## Genesis Bararite is a secondary mineral of sublimational origin. It forms under specific conditions, most often in zones of underground fires in coal mines or on burning coal mine dumps. It forms as a result of the reaction of gaseous hydrogen fluoride (derived from the decomposition of clay minerals) with ammonia (produced by coal combustion) at temperatures below 15°C. ## Mineral Associations It co-occurs with other minerals formed under similar conditions, such as sal ammoniac, native sulfur, cryptohalite, and mascagnite. ## Localities The most important bararite localities worldwide include the discovery site in the Barari mine in India; Vesuvius in Italy; burning dumps in Pennsylvania (USA), particularly in Northumberland County; as well as in coal mines in Russia (Chelyabinsk) and Germany (Saxony).
Rarity
Rare
For collectors
## Quality Criteria For collectors, the abundance and purity of the bararite coating on the rock matrix are most important. Specimens with clearly visible, though fine, crystalline aggregates are more valued. Association with other rare minerals from the same paragenesis, e.g., sal ammoniac, is also important. ## Popular Localities The most known and valued specimens come from classic localities for this type of mineral, namely the burning dumps in Pennsylvania, USA, and the vicinity of Vesuvius in Italy.
Care and storage
## Cleaning Bararite is water-soluble, so it must absolutely not be cleaned with water. To remove dust, a very soft, dry brush or compressed air from a safe distance can be used with extreme caution. ## What to Avoid Any contact with water, water vapor, and other liquids should be avoided. The mineral is very sensitive to moisture and can completely dissolve. It should be protected from high temperatures, which can cause its transformation into cryptohalite. ## Storage Bararite specimens must be stored in sealed, dry containers, preferably with a desiccant (e.g., silica gel). They should be displayed away from sources of heat and moisture, in stable temperature conditions.