Vuonnemite
Chemical formula: Na<sub>6</sub>Na<sub>2</sub>Nb<sup>5+</sup><sub>2</sub>Na<sub>3</sub>Ti<sup>4+</sup>(Si<sub>2</sub>O<sub>7</sub>)<sub>2</sub>(PO<sub>4</sub>)<sub>2</sub>O<sub>2</sub>(OF)
Vuonnemite is a rare sodium, niobium, and titanium silicate and phosphate, forming tabular crystals with a pearly luster.
Properties
- Mohs hardness
- 2-3
- Luster
- Pearly, Vitreous, Greasy
- Streak
- White
- Density
- 3.14
- Cleavage
- Perfect on {001}
- Fracture
- Uneven
- Transparency
- Translucent, Translucent
- Crystal system
- Triclinic
Diagnostic features
## Identification Key diagnostic features of vuonnemite include its tabular habit, perfect cleavage in one direction, pearly luster on cleavage surfaces, and low hardness. Its instability in water is also characteristic. ## Distinguishing from similar minerals Vuonnemite can be confused with other minerals with a tabular habit and pearly luster, such as micas (e.g., muscovite) or lomonosovite. It differs from micas by its lower hardness and instability in water. Lomonosovite is very similar, but vuonnemite is a product of its alteration and often forms intergrowths with it. Accurate identification requires advanced methods, such as X-ray diffraction (XRD). ## Crystal Forms Vuonnemite forms well-developed, tabular or lamellar crystals, often gathered in subparallel or radial aggregates. Crystals are usually elongated and may have a pseudohexagonal outline.
Geological environment
## Genesis Vuonnemite is a mineral of magmatic origin, crystallizing in the late stages from strongly alkaline, sodium- and rare-element-saturated nepheline syenite pegmatites. It also forms as a metasomatic product in rocks surrounding these pegmatites. ## Mineral Associations This mineral often co-occurs with other rare minerals of alkaline massifs, such as lomonosovite (from which it can form through alteration), eudialyte, nepheline, microcline, aegirine, lamprophyllite, murmanite, and sphalerite. ## Localities The most important and well-known localities for vuonnemite are in Russia, in the alkaline massifs of the Kola Peninsula – Khibiny (Koashva Mountain, Eveslogchorr) and Lovozero (Karnasurt Mountain, Kedykvyrpakhk). Outside Russia, its occurrence has been reported in the Ilímaussaq complex in Greenland and at Mont Saint-Hilaire in Quebec, Canada.
Rarity
Rare
For collectors
## Quality Criteria The most prized specimens by collectors are those with well-formed, sharply terminated crystals of large size and strong luster. The aesthetic arrangement of crystals on the rock matrix and the presence of rare associated minerals also enhance their appeal. Purity and absence of mechanical damage are crucial, given the mineral's brittleness and perfect cleavage. ## Popular Localities Undoubtedly, the best and largest vuonnemite crystals come from the pegmatites of the Khibiny Massif, especially from the Koashva mine on the Kola Peninsula in Russia. Specimens from Mont Saint-Hilaire and Ilímaussaq are usually much smaller but are also sought after by specialists.
Care and storage
## Cleaning Due to its low hardness and perfect cleavage, vuonnemite requires very careful handling. Cleaning should be limited to gentle dusting with a soft brush. The use of water is not recommended, as the mineral is unstable in water and can decompose. ## What to avoid Contact with water, acids, and other chemicals must be strictly avoided. The mineral is sensitive to moisture and temperature changes. It should not be cleaned with ultrasonics or steam. It should be protected from impacts and scratches. ## Storage Vuonnemite specimens should be stored in a dry place, preferably in an airtight container with a desiccant (e.g., silica gel). To prevent mechanical damage, it should be stored in a separate, padded compartment, away from harder minerals.