Frankamenite

Chemical formula: K<sub>3</sub>Na<sub>3</sub>Ca<sub>5</sub>Si<sub>12</sub>O<sub>30</sub>F<sub>3</sub>(OH)·H<sub>2</sub>O

Frankamenite is a rare silicate with a complex composition, forming purple, fibrous or lamellar aggregates with a pearly luster.

## Characteristics Frankamenite is a complex potassium, sodium, and calcium silicate from the canasite group. It occurs in fibrous, lamellar, or radial aggregates, which can reach up to 2 cm in diameter. Its characteristic features are a purple or lilac color and a distinct, pearly luster on cleavage surfaces. ## Physical Properties This mineral has a hardness of approximately 5 on the Mohs scale. It exhibits perfect cleavage in one direction, which, combined with its fibrous structure, makes it brittle. The luster is vitreous, and on cleavage planes, it is pearly. It is a translucent mineral. ## Colors and Varieties Frankamenite occurs in shades of purple, from pale lilac to intense purple. No commercial or color varieties have been distinguished. ## History and Name The mineral's name honors Victor Albertovich Frank-Kamenetsky (1915–1994), a Russian crystallographer and mineralogist from St. Petersburg University. It was recognized as a new mineral by the IMA in 1996. ## Uses Frankamenite has no industrial applications. It is solely a mineral of scientific and collector's interest.

Properties

Mohs hardness
5
Luster
Vitreous, Pearly
Streak
White
Density
2.75
Cleavage
Perfect on {100}
Fracture
Splintery
Transparency
Translucent
Crystal system
Triclinic

Diagnostic features

## Identification Frankamenite can be identified by its characteristic purple color, fibrous or lamellar structure, and pearly luster on cleavage surfaces. It is relatively soft (approximately 5 on the Mohs scale). ## Distinguishing from Similar Minerals It can be confused with charoite, which also has a purple color and fibrous structure. Frankamenite differs from it by its association with other minerals from the Murun massif (e.g., aegirine, tinaksite) and subtle differences in hue and luster. Precise identification requires advanced studies, such as XRD. ## Crystal Forms It forms elongated, lamellar crystals, most often occurring as radial or tangled aggregates. Granular forms are less common.

Geological environment

## Genesis Frankamenite is a metasomatic mineral. It forms in alkali-rich rocks as a result of hydrothermal solutions interacting with sedimentary rocks (carbonates) in contact zones with syenite intrusions. ## Mineral Associations It most commonly co-occurs with microcline, aegirine, quartz, tinaksite, canasite, and charoite. It is one of the charoite-bearing minerals from the Murun massif rocks. ## Localities The only confirmed locality of frankamenite in the world is the Murun massif (Tausonitovy Tract), located on the border of the Irkutsk Oblast and Yakutia (Sakha Republic) in Russia. This is the type locality for this mineral.

Rarity

Very rare

For collectors

## Quality Criteria The most valued specimens by collectors are those with well-formed, radial aggregates of intense, purple color. Aesthetic composition with other associated minerals, such as green aegirine or orange tinaksite, is also important. Purity and lack of damage to delicate fibers significantly increase the specimen's value. ## Popular Localities The only source of frankamenite specimens is the Murun massif in Russia, which is also the sole locality for charoite. Specimens from this locality are unique on a global scale.

Care and storage

## Cleaning Frankamenite specimens should be cleaned only with extreme caution, using a soft brush to remove dust. Due to its perfect cleavage and fibrous nature, washing in water, and especially mechanical and ultrasonic cleaning, should be avoided. ## What to Avoid Avoid contact with chemicals, acids, and detergents. The mineral is brittle and sensitive to impacts and pressure. It should not be heated or exposed to sudden temperature changes. ## Storage Collector's frankamenite specimens are best stored in closed display boxes, separated from harder minerals to prevent scratches and mechanical damage. Due to its brittleness, it is not suitable for display in areas prone to vibrations or touch.

External references

Sources

Read more