Lecontite
Chemical formula: (N<sup>3-</sup>H<sub>4</sub>)Na(S<sup>6+</sup>O<sub>4</sub>)·2H<sub>2</sub>O
Lecontite is a rare, water-soluble sodium-ammonium sulfate, forming colorless or white, acicular crystals in ammonia-rich environments.
Properties
- Mohs hardness
- 2-2.5
- Luster
- Vitreous
- Streak
- White
- Density
- 1.643
- Cleavage
- Perfect on {010}, Good on {110}
- Fracture
- Conchoidal
- Transparency
- Transparent to translucent
- Crystal system
- Orthorhombic
Diagnostic features
## Identification The key diagnostic feature of lecontite is its complete and rapid solubility in water. A characteristic salty and bitter taste is also present. It occurs as delicate, acicular or fibrous crystals in specific, dry environments, such as guano caves. ## Distinguishing from Similar Minerals Lecontite can be confused with other soluble sulfates, such as epsomite, mirabilite, or thenardite. It is distinguished by the presence of the ammonium ion, which can be confirmed by chemical tests (ammonia release upon contact with bases). Visually, it can resemble some zeolites, but the water solubility test is decisive. ## Crystal Forms Lecontite crystallizes in the orthorhombic system, forming short, prismatic or acicular crystals. It is most commonly found as delicate, radiating or fibrous aggregates and crusts.
Geological environment
## Genesis Lecontite is a secondary mineral, formed by the reaction of sulfate-rich solutions with ammonia derived from the decomposition of organic matter. Its typical formation environment is bat or bird guano deposits in dry caves and on islands. It can also crystallize as a sublimation product in volcanic fumaroles. ## Mineral Associations This mineral co-occurs with other sulfates and nitrates formed under similar conditions, such as mascagnite, thenardite, mirabilite, gypsum, syngenite, as well as with nitratine and niter. ## Locations The most important lecontite localities are caves with guano deposits. It was discovered in the Las Piedras cave in Honduras. It also occurs on the Chincha Islands in Peru, in the Friesland mine in Saxony (Germany), and as a product of fumarolic activity on Vesuvius and Etna in Italy.
Rarity
Rare
For collectors
## Quality Criteria The most prized lecontite specimens are those with well-formed, transparent crystals, forming attractive, radiating aggregates on a rock matrix. Due to the mineral's instability, it is crucial that the specimen is well-preserved and stable. Crystal size and the aesthetics of the overall composition significantly influence its value. ## Popular Localities Specimens from classic localities, such as the Chincha Islands in Peru, are historically important, although rarely available on the market. Currently, small quantities of collector material may come from various dry caves worldwide.
Care and storage
## Cleaning This mineral should not be cleaned wet, as it is completely soluble in water. To remove dust, a very soft, dry brush or compressed air from a distance can be used very carefully. ## What to Avoid Contact with water, water vapor, and all liquids must be absolutely avoided. Lecontite is hygroscopic, so it absorbs moisture from the air, leading to its disintegration. It must be protected from high humidity, temperature changes, and direct sunlight. ## Storage Lecontite specimens must be stored in sealed, airtight containers (e.g., "perky box" type) with a desiccant (e.g., silica gel). Display is only possible under such conditions, away from sources of moisture and heat.