Frankamenite is the

fluorine Fluorine is a chemical element with the symbol F and atomic number 9. It is the lightest halogen and exists at standard conditions as a highly toxic, pale yellow diatomic gas. As the most electronegative reactive element, it is extremely reactiv ...

-dominate variation of the rare

mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. (2 ...

canasite with a general formula of K₃Na₃Ca₅(Si₁₂O₃₀) ,(OH)sub>4·(H₂O). Frankamenite belongs to the

triclinic 180px, Triclinic (a ≠ b ≠ c and α ≠ β ≠ γ ) In crystallography, the triclinic (or anorthic) crystal system is one of the 7 crystal systems. A crystal system is described by three basis vectors. In the triclinic system, the crystal i ...

crystal system In crystallography, a crystal system is a set of point groups (a group of geometric symmetries with at least one fixed point). A lattice system is a set of Bravais lattices. Space groups are classified into crystal systems according to their poin ...

, with the bases of its structure containing Ca-Na mixed octahedra joined by octagonal tubes SiO₄ of the composition (Si₁₂O₃₀). Frankamenite has six Ca-Na mixed positions distributed amongst these octahedra, reflecting its varying compositions. Frankamenite was named for the Russian

mineralogist Mineralogy is a subject of geology specializing in the scientific study of the chemistry, crystal structure, and physical (including optical) properties of minerals and mineralized artifacts. Specific studies within mineralogy include the proce ...

- crystallographer V. A. Frank-Kamentsky (1915–1994), who discovered the mineral. Frankamenite occurs in association with the rare mineral

charoite Charoite is a rare silicate mineral, first described in 1978. It was believed to be named after the Chara River, but due to the river being 70 km away from its discovery place, now it is believed to be named after the Russian word ''chary'', ...

, which is found only in the

Murun Massif Murun (russian: Мурун) is a mountain in the Olyokma-Chara Plateau, at the border of Irkutsk Oblast and Yakutia, Russian Federation. Geography A high summit is the highest point of the Murun Massif in the Olyokma-Chara Plateau, part of th ...

of the Olyokma-Chara Plateau, Aldan Shield,

Sakha Republic Sakha, officially the Republic of Sakha (Yakutia),, is the largest republic of Russia, located in the Russian Far East, along the Arctic Ocean, with a population of roughly 1 million. Sakha comprises half of the area of its governing Far E ...

Yakutia Sakha, officially the Republic of Sakha (Yakutia),, is the largest republic of Russia, located in the Russian Far East, along the Arctic Ocean, with a population of roughly 1 million. Sakha comprises half of the area of its governing Far E ...

Siberia Siberia ( ; rus, Сибирь, r=Sibir', p=sʲɪˈbʲirʲ, a=Ru-Сибирь.ogg) is an extensive geographical region, constituting all of North Asia, from the Ural Mountains in the west to the Pacific Ocean in the east. It has been a part ...

Russia Russia (, , ), or the Russian Federation, is a transcontinental country spanning Eastern Europe and Northern Asia. It is the largest country in the world, with its internationally recognised territory covering , and encompassing one-ei ...

. Here,

metasomatism Metasomatism (from the Greek μετά ''metá'' "change" and σῶμα ''sôma'' "body") is the chemical alteration of a rock by hydrothermal and other fluids. It is the replacement of one rock by another of different mineralogical and chemical co ...

enriches a

syenite Syenite is a coarse-grained intrusive igneous rock with a general composition similar to that of granite, but deficient in quartz, which, if present at all, occurs in relatively small concentrations (< 5%). Some syenites contain larger prop ...

massif In geology, a massif ( or ) is a section of a planet's crust that is demarcated by faults or flexures. In the movement of the crust, a massif tends to retain its internal structure while being displaced as a whole. The term also refers to a ...

with

potassium Potassium is the chemical element with the symbol K (from Neo-Latin '' kalium'') and atomic number19. Potassium is a silvery-white metal that is soft enough to be cut with a knife with little force. Potassium metal reacts rapidly with atmos ...

when it comes into contact with a

limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms w ...

at around 200–250 °C. This metamorphic process produces a

potassium feldspar Potassium feldspar refers to a number of minerals in the feldspar group, and containing potassium: *Orthoclase ( endmember formula K Al Si3 O8), an important tectosilicate mineral that forms igneous rock *Microcline, chemically the same as orthocla ...

metasomatite, the typical geological environment for canasite and, therefore, frankamenite. Frankamenite and charoitein are exclusive to the Sakha Republic in this sort of environment, as mineralogists have yet to discover the minerals elsewhere.Charoite on Webmineral
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References

Calcium minerals Inosilicates Potassium minerals Sodium minerals Triclinic minerals Minerals in space group 1 {{silicate-mineral-stub