Natrophosphate
Chemical formula: Na<sub>7</sub>(PO<sub>4</sub>)<sub>2</sub>F·19H<sub>2</sub>O
A very rare, water-soluble sodium phosphate, forming colorless, isometric crystals in alkaline pegmatites.
Description
## Characteristics Natrophosphate is a hydrated sodium fluoride and phosphate, known for forming well-developed, vitreous crystals. Typical specimens consist of transparent, colorless crystals in the form of rhombic dodecahedra, less commonly cubes. This mineral is extremely unstable under atmospheric conditions – it readily absorbs water and undergoes alteration, losing its original transparency and luster. ## Physical Properties It is characterized by low hardness of 2.5 on the Mohs scale and a low density of approximately 2.36 g/cm³. It has a vitreous luster on fresh surfaces, which quickly dulls upon exposure to air. It is transparent to translucent. Its most characteristic features are perfect cleavage in three directions and complete solubility in water. ## Colors and Varieties Natrophosphate is usually colorless or white. Sometimes it is tinged with a delicate, yellowish hue. It does not form colored or commercial varieties. ## History and Name The mineral's name, given in 1972, directly refers to its chemical composition – a high content of sodium (Latin: *natrium*) and the presence of the phosphate group. It was discovered and described based on specimens found in ultra-alkaline pegmatites of the Khibiny Massif on the Kola Peninsula in Russia. ## Uses Due to its rarity and, most importantly, its instability, natrophosphate has no industrial applications. It is solely an object of scientific interest and a prized acquisition for advanced systematic and regional mineral collections.
Diagnostic features
## Identification Key diagnostic features of natrophosphate are its isometric crystallographic form (dodecahedra), low hardness, vitreous luster on fresh surfaces, and perfect cleavage. The most important test is its reaction to moisture – the mineral dulls and becomes covered with a white coating, and upon contact with a drop of water, it completely dissolves. ## Distinguishing from Similar Minerals It can be confused with other colorless, water-soluble minerals from alkaline parageneses, such as thermonatrite or natron. Its isometric crystal system and crystal habit distinguish it from them. Halite (rock salt) is also isometric and soluble, but has a different taste and perfect cleavage along cubic faces {100}, whereas natrophosphate exhibits cleavage along dodecahedral planes {110}. ## Crystal Forms It most often forms single, well-developed crystals in the shape of a rhombic dodecahedron {110}. Less common are cubes {100} or forms that are a combination of both. It also occurs as granular aggregates.
Geological environment
## Genesis Natrophosphate is a hydrothermal mineral, crystallizing in the late stages of pegmatite formation within nepheline syenite massifs. It forms in vugs and fractures from solutions rich in sodium, phosphorus, and fluorine. ## Mineral Associations It often co-occurs with a range of rare alkaline minerals, such as ussingite, natrosilite, williaumite, thermonatrite, aegirine, lomonosovite, kazakovite, and vuonnemite. The presence of these minerals is a strong indicator of an environment conducive to natrophosphate formation. ## Localities The most important and classic localities for this mineral are in Russia, on the Kola Peninsula, in the Khibiny Massif (Mount Rasvumchorr, Kuniyok) and Lovozero Massif (Mount Alluaiv). It is also known from the Ilimaussaq complex in Greenland and the famous Mont Saint-Hilaire locality in Quebec, Canada.
Rarity
Very rare
Collector aspects
## Quality Criteria The most highly valued specimens are those with large, sharp, fully transparent, and undamaged crystals. The absence of weathering signs is crucial – surfaces should be shiny, not dull or covered with a white coating. The attractiveness of a specimen is enhanced by its placement on a contrasting matrix, for example, on dark aegirine crystals. ## Popular Localities Specimens from the Khibiny and Lovozero Massifs on the Kola Peninsula are considered the global standard for this mineral and fetch the highest prices in the collector's market.
Care and storage
## Cleaning The mineral is completely soluble in water, so contact with any liquid is absolutely forbidden. To remove dust, only a soft, dry brush should be used, or dust should be carefully blown off with compressed air from a safe distance. ## What to Avoid Avoid contact with water, water vapor, and humid air, which cause it to dissolve or transform into white, powdery secondary minerals. It is sensitive to elevated temperatures, which accelerate the dehydration process. It should be protected from all chemicals. ## Storage Natrophosphate specimens require storage in sealed, airtight containers (e.g., "perky box" type) away from sources of moisture. It is advisable to place a desiccant (e.g., silica gel) in the container. Avoid exposure to direct sunlight and sudden temperature changes.