Ammonioborite
Chemical formula: (N<sup>3-</sup>H<sub>4</sub>)<sub>3</sub>B<sub>15</sub>O<sub>20</sub>(OH)<sub>8</sub>·4H<sub>2</sub>O
Ammonioborite is a rare hydrated ammonium borate, forming small, colorless crystals and aggregates in geothermal environments.
Properties
- Mohs hardness
- 3
- Luster
- Vitreous
- Streak
- White
- Density
- 1.89
- Cleavage
- Perfect on {010}
- Fracture
- Uneven
- Transparency
- Transparent to Translucent
- Crystal system
- Monoclinic
Diagnostic features
## Identification A key diagnostic feature of ammonioborite is its reaction to water – the mineral dissolves in it. It occurs as small, colorless or white crystals, often in radial aggregates. Its low hardness and occurrence in a specific geothermal environment are also important clues. ## Distinguishing from Similar Minerals It can be confused with other borates found in similar environments, such as Larderellite, with which it often co-occurs. However, Larderellite has a different crystal habit (typically small, tetragonal plates) and different optical properties. Final differentiation usually requires chemical or crystallographic analysis. ## Crystal Forms Ammonioborite crystallizes as small, tabular or bladed crystals, rarely exceeding 1 mm in length. Most often, it forms radial or stellate aggregates, as well as spherulites and granular groupings.
Geological environment
## Genesis Ammonioborite is a mineral of sedimentary origin, formed by the evaporation of geothermal waters rich in boron and ammonia. It forms in hot springs and fumaroles, crystallizing directly from aqueous solutions at temperatures below 55°C. ## Mineral Associations It most commonly co-occurs with Larderellite, another ammonium borate. It is also accompanied by Sassolite (natural boric acid) and native sulfur. ## Localities The most important and classic locality for ammonioborite is the geothermal fields in Larderello, Tuscany, Italy. This is its type locality. It has also been reported in other geothermal areas, for example, in the Geyzernaya Valley on the Kamchatka Peninsula in Russia.
Rarity
Very rare
For collectors
## Quality Criteria The quality of ammonioborite specimens primarily depends on the size and development of the crystals and the aesthetics of the aggregates. Specimens with distinct, radial or spherulitic groupings of well-formed crystals are most valued. Due to its rarity and small size, any well-defined specimen is valuable for collectors specializing in rare minerals or minerals from specific localities. ## Popular Localities The only source of collector specimens of historical and reference importance is Larderello in Tuscany, Italy. Specimens from this location are most sought after by collectors.
Care and storage
## Cleaning Ammonioborite specimens should be cleaned only very carefully, using compressed air to remove dust. Contact with water is absolutely inadvisable, as the mineral is soluble in it. ## What to Avoid All contact with water, water vapor, and other liquids should be avoided. The mineral is sensitive to moisture and can be damaged or completely dissolved. It should also be protected from high temperatures and chemicals. ## Storage Storage requires an environment with controlled, low humidity. It is best to place the specimen in a sealed, airtight container (a "perky box") along with a desiccant, such as silica gel. Exposure to open air should be avoided.