Limousinite
Chemical formula: BaCa[Be<sub>4</sub>P<sub>4</sub>O<sub>16</sub>]·6H<sub>2</sub>O
Limousinite is a hydrated barium calcium beryllophosphate, forming colorless, prismatic crystals with a vitreous luster.
Properties
- Mohs hardness
- 5
- Luster
- Vitreous
- Streak
- White
- Density
- 2.75
- Cleavage
- None
- Fracture
- Uneven
- Transparency
- Transparent
- Crystal system
- Tetragonal
Diagnostic features
## Identification Limousinite is difficult to identify visually without specialized equipment. It is recognized by its crystal form – small, colorless, prismatic needles – and by its specific occurrence environment in granitic pegmatites. Vitreous luster and lack of cleavage are auxiliary features. Final identification requires advanced analytical methods such as Raman spectroscopy or X-ray diffraction (XRD) combined with chemical analysis (EDS). ## Distinguishing from Similar Minerals It can be confused with other colorless, acicular secondary minerals found in pegmatites, such as some zeolites or other rare phosphates. It is distinguished from zeolites by its greater hardness. Certain differentiation from other beryllophosphates, such as babefphite or herderite, is almost exclusively possible through chemical and crystallographic analysis. ## Crystal Forms Limousinite crystals are prismatic, elongated along the [001] axis, and terminated by a pyramid. They typically form radial or chaotically arranged aggregates of tiny needles on the surface of other minerals, mainly on quartz or albite.
Geological environment
## Genesis Limousinite is a hydrothermal mineral, crystallizing in the late stage of granitic pegmatite evolution. It forms in vugs and fissures as a result of the alteration of primary beryllium minerals (such as beryl) and phosphates (such as apatite) under the influence of barium- and calcium-rich solutions. ## Mineral Associations This mineral co-occurs with quartz (often smoky), albite, microcline, muscovite, beryl, apatite, fluorite, hematite, and other rare phosphates such as babefphite, väyrynenite, and beryllonite. ## Localities The only confirmed and described occurrence of limousinite in the world is its type locality – the Vilatte quarry in Chanteloube, near Nantiat in the Haute-Vienne department (Limousin region), France.
Rarity
Extremely rare
For collectors
## Quality Criteria The most valuable limousinite specimens are those with well-formed, transparent crystals forming rich, radial aggregates on a contrasting matrix, for example, on smoky quartz. Due to the microscopic size of the crystals, their abundance and aesthetic arrangement on the matrix are crucial. Specimens with a well-defined association of other rare phosphate minerals are also more highly valued. ## Popular Localities The only source of limousinite specimens is the Vilatte quarry in Chanteloube, France. Material from this locality is extremely rare and sought after by specialized systematic mineral collectors and "micromount" enthusiasts.
Care and storage
## Cleaning Limousinite specimens should be cleaned very carefully, using a soft brush to remove dust. Due to its brittleness and potential reactivity, wet cleaning, especially with detergents, is not recommended. If liquid is necessary, use only distilled water or isopropyl alcohol, applying minimal amounts and quickly drying the specimen. ## What to Avoid Avoid contact with acids and other chemicals that can damage the mineral. Limousinite is a hydrated mineral, so it should be protected from high temperatures, which could cause dehydration and destruction of its structure. Ultrasonic cleaning devices should also be avoided. ## Storage Collectible limousinite specimens, due to their small size and fragility, are best stored in sealed "micromount" boxes, which protect them from mechanical damage and dust. They should be kept in stable humidity and temperature conditions, away from direct sunlight.