Selsurtite
Chemical formula: (H<sub>3</sub>O)<sub>12</sub>Na<sub>3</sub>(Ca<sub>3</sub>Mn<sup>2+</sup><sub>3</sub>)(Na<sub>2</sub>Fe<sup>2+</sup>)Zr<sup>4+</sup><sub>3</sub>☐Si[Si<sub>24</sub>O<sub>69</sub>(OH)<sub>3</sub>](OH)Cl·H<sub>2</sub>O
Selsurtite is a very rare, complex cyclosilicate of the eudialyte group, characterized by its unique chemical composition and occurrence in a single locality worldwide.
Properties
- Mohs hardness
- 5
- Luster
- Vitreous
- Streak
- White
- Density
- 2.91
- Cleavage
- None
- Fracture
- Uneven
- Transparency
- Translucent
- Crystal system
- Trigonal
Diagnostic features
## Identification Amateur identification of selsurtite is practically impossible. A key clue is its origin from pegmatites in the Khibiny Massif. Brown color, granular form, and vitreous luster combined with characteristic parageneses (co-occurrence with aegirine, nepheline, lorenzenite) may suggest the presence of a mineral from the eudialyte group. Definitive identification requires advanced analytical methods, such as X-ray diffraction (XRD) and chemical microanalysis (EDS/WDS). ## Distinguishing from Similar Minerals Selsurtite is visually indistinguishable from other brown minerals of the eudialyte group, such as monoclinic oneillite or raslakite. The differences between them lie in subtle changes in chemical composition and crystal symmetry, which can only be detected in a laboratory. ## Crystal Forms Selsurtite crystallizes in the trigonal system. It is most commonly found as aggregates of irregularly shaped grains. Less frequently, it forms imperfectly developed, small crystals with rhombohedral outlines.
Geological environment
## Genesis Selsurtite is a magmatic mineral, crystallizing in the late stages of evolution of highly alkaline, volatile-element-saturated pegmatites. It forms under hyperagpaitic conditions, characterized by an extremely high alkali-to-aluminum ratio. ## Mineral Associations This mineral occurs in association with other rare minerals typical of the Khibiny Massif pegmatites. The most common associations include: aegirine, potassium feldspar, nepheline, lamprophyllite, lorenzenite, sodalite, and other minerals of the eudialyte group. ## Localities The only confirmed locality of selsurtite worldwide is its type locality – Mount Koashva in the Khibiny Massif on the Kola Peninsula in the Murmansk Oblast, Russia.
Rarity
Extremely rare
For collectors
## Quality Criteria The quality of selsurtite specimens, which are almost exclusively microminerals, is assessed based on several criteria. The most important are the abundance of the mineral on the rock matrix and the degree of crystal development, even if they are imperfect. Specimens with rich and aesthetic associations of other rare minerals are also highly valued, especially if they form well-defined crystals. ## Popular Localities All known selsurtite specimens come from a single locality – the pegmatites on Mount Koashva in the Russian Khibiny Massif. This is a classic locality for many rare alkaline minerals, and specimens from there are a hallmark of this mineralogical province.
Care and storage
## Cleaning Selsurtite specimens should be cleaned with great care, preferably dry, using a soft brush to remove dust. If necessary, a moistened cotton swab with distilled water can be used, followed by thorough drying of the specimen. Ultrasonic cleaners should be avoided. ## What to Avoid This mineral is potentially sensitive to acids and strong chemicals. It should be protected from high temperatures, which could damage its structure through water loss. Prolonged exposure to direct sunlight is not advisable. ## Storage Collectible selsurtite specimens, typically in the form of microminerals, should be stored in sealed, padded "micromount" boxes to protect them from mechanical damage and dust. Store in stable room conditions.