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.
Properties
- Mohs hardness
- 2.5
- Luster
- Vitreous
- Streak
- White
- Density
- 2.36
- Cleavage
- Perfect on {111}
- Fracture
- Conchoidal
- Transparency
- Transparent to translucent
- Crystal system
- Isometric
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
For collectors
## 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.