CHIOLITE

Chiolite is a rare tetragonal sodium aluminium fluoride mineral with chemical formula Na₅Al₃F₁₄, IMA symbol Cio, Strunz classification 03.CE.05, Dana classification 11.06.11.01, space group P4/mnc, molecular weight 461.87 g/mol, CAS number 1302-84-7, EC number 215-112-7, specific gravity 2.998 g/cm³, and Mohs hardness 2.5 (revised from the historically cited 3.5–4, per Pauly 1985); it occurs as nearly colourless to snow-white, mostly granular or massive aggregates and rarely as distinct dipyramidal crystals up to 10 cm in length, and derives its name from the Greek χιών (chion, snow) and λίθος (lithos, stone) in allusion to its resemblance to cryolite (ice-stone).
Chiolite is the high-fluoride polymorph of the sodium aluminium fluoride system, compositionally containing Na 24.89%, Al 17.53%, and F 57.59%; it occurs exclusively in granite pegmatites under fluorine-rich geochemical conditions in association with cryolite, topaz, fluorite, thomsenolite, pachnolite, elpasolite, cryolithionite, ralstonite, phenakite, pyrite, chalcopyrite, jarlite, and sericite; it was first described in 1846 by Hermann and Auerbach from the Miask district of the Ilmen Mountains, Ural, Russia, making it a pre-IMA valid species grandfathered by the IMA.
Natural chiolite is extremely rare and almost never cut as a gemstone — fewer than two dozen faceted specimens are estimated to exist worldwide — but synthetic chiolite has attracted significant industrial and research interest as a precursor in aluminium metallurgy, as a flux in ceramic and glass manufacture, and most recently (Journal of Molecular Structure, January 2025) as a lanthanide-activated UVB-emitting phosphor host lattice for applications in medical phototherapy, UV curing, and anti-theft security systems.

Chemical Formula: Na₅Al₃F₁₄
IMA Symbol: Cio
CAS Number: 1302-84-7
EC Number: 215-112-7
Molecular Weight: 461.87 g/mol

Synonyms: Chiolite, Arksutite, Arksudite, Chodneffite, Chodnewite, Nipholith, Chiolithe, Sodium aluminium fluoride, Pentasodium tris(tetrafluoroaluminate), Na₅Al₃F₁₄, EINECS 215-112-7, PubChem CID 71300915, RefChem:125212, Chiolite (Na₅(Al₃F₁₄)), ICSD 126419, CAS 1302-84-7

Chiolite is identified by IUPAC name pentasodium;bis(pentafluoroaluminum(2−));tetrafluoroalumanuide, SMILES F[Al-](F)(F)F.F[Al-2](F)(F)(F)F.F[Al-2](F)(F)(F)F.[Na+].[Na+].[Na+].[Na+].[Na+], InChI=1S/3Al.14FH.5Na/h;;;14*1H;;;;;/q3*+3;;;;;;;;;;;;;;;5*+1/p-14, InChIKey PPPLOTGLKDTASM-UHFFFAOYSA-A; PubChem CID 71300915, exact mass 461.871106 Da, heavy atom count 22, HBA 17, HBD 0, rotatable bonds 0, covalently-bonded units 8, complexity 56.2.

Composed of sodium, aluminium, and fluorine, Chiolite has the ideal chemical formula Na₅Al₃F₁₄.
The formula of Chiolite corresponds to a molecular weight of approximately 461.87 g/mol.

Within mineral classification systems, Chiolite belongs to the sodium aluminium fluoride group.
A different sodium-to-aluminium ratio distinguishes Chiolite from the chemically related mineral cryolite.

Natural crystals of Chiolite usually appear nearly colourless or snow-white.
Vitreous, pearly, or slightly greasy lustres may develop on different surfaces of Chiolite.

A Mohs hardness near 2.5 makes Chiolite a relatively soft mineral.
With a specific gravity close to 3.0, Chiolite remains considerably denser than water.

Chiolite crystallises in the tetragonal crystal system.
Dipyramidal, tabular, and occasionally distorted prismatic forms can occur in Chiolite.

Perfect basal cleavage allows Chiolite to separate readily along the {001} plane.
An additional distinct cleavage direction contributes to the characteristic breakage pattern of Chiolite.

Transparent to translucent specimens are common among well-formed crystals of Chiolite.
Low birefringence and uniaxial negative optical behaviour characterise Chiolite under polarised light.

Sheets of corner-sharing aluminium fluoride octahedra form an important part of the crystal structure of Chiolite.
Layers containing sodium fluoride octahedra occur between the aluminium-rich sheets in Chiolite.

Natural deposits commonly associate Chiolite with cryolite and other fluoride minerals.
Granite pegmatites and specialised fluoride-rich geological environments may host Chiolite.

The Ilmen Mountains of Russia provided the first described specimens of Chiolite in the nineteenth century.
Notable occurrences of Chiolite have also been recorded in Greenland and Virginia in the United States.

The name Chiolite originates from Greek words referring to snow and stone.
Its snow-white appearance inspired the mineral name Chiolite.

Because natural material remains uncommon, industrial applications generally rely on synthetic Chiolite.
Controlled production gives synthetic Chiolite a consistent composition and predictable phase purity.

Synthetic Chiolite commonly appears as a white to off-white inorganic powder.
Water does not readily dissolve Chiolite under normal conditions.

Reaction between cryolite and aluminium fluoride can generate Chiolite under suitable thermal conditions.
Precipitation and solid-state synthesis routes can also produce high-purity Chiolite.

In aluminium electrolysis, Chiolite can occur as a component of the fluoride-based molten bath.
Addition of Chiolite helps adjust the sodium-to-aluminium fluoride balance of aluminium-smelting electrolytes.

A melting temperature near 730°C allows Chiolite to participate in lower-temperature fluoride bath systems.
Molten-bath chemistry can be modified by the amount and phase distribution of Chiolite.

Solidified electrolyte from aluminium cells may contain Chiolite together with cryolite and other fluoride phases.
X-ray diffraction can identify Chiolite during analysis and control of aluminium electrolysis baths.

Recovery processes can treat Chiolite-containing bath materials as a source of aluminium fluoride.
Recycling Chiolite-bearing electrolyte residues supports improved use of fluoride resources.

Glass and ceramic formulations may use Chiolite as a source of sodium, aluminium, and fluoride.
Fluxing behaviour provided by Chiolite can influence melting and surface development in specialised compositions.

Enamel formulations can incorporate Chiolite to modify fusion and opacity characteristics.
Carefully controlled additions of Chiolite help adjust the firing behaviour of fluoride-containing enamel systems.

Brazing and welding fluxes may employ Chiolite as a double fluoride of sodium and aluminium.
During metal joining, Chiolite can support oxide removal and improve the wetting behaviour of the molten filler.

Materials research uses Chiolite as a model compound for studying fluoride crystal structures and phase transitions.
X-ray diffraction, fluorine NMR, and aluminium NMR provide complementary methods for characterising Chiolite.

Uses of Chiolite:
Synthetic chiolite (Na₅Al₃F₁₄) is used as a flux and bath additive in aluminium electrolysis (Hall–Héroult process), where it lowers the melting point of the aluminium oxide–cryolite melt, reduces energy consumption, and improves the conductivity of the electrolytic bath; it functions analogously to cryolite (Na₃AlF₆) but has a higher aluminium fluoride content (molar ratio AlF₃:NaF = 1:1.67 for chiolite vs 1:3 for cryolite).
Chiolite is used as a raw material in the production of aluminium fluoride (AlF₃), sodium fluoride (NaF), and other fluorine-containing compounds, and as a flux in the manufacture of specialty ceramics and glass where it lowers the fusion temperature and improves the flow of silicate melts.
Synthetic chiolite doped with lanthanide ions — specifically Ce³⁺ and Gd³⁺ — has been demonstrated (2025) as a UVB-emitting phosphor host lattice; UVB phosphors are used in medical phototherapy for skin conditions including psoriasis, eczema, and vitiligo, as well as in UV polymer and resin curing, tanning beds, and anti-theft security tags, opening a new application domain for the chiolite structure type.
Natural chiolite serves as a reference mineral and geological index species for fluorine-rich granite pegmatite systems; it is used as an analytical reference standard and characterisation material in mineralogical research, including NMR-combined powder X-ray diffraction structure determination (chiolite was selected as a test case for developing a general inorganic structure-solution approach from powders).
Historically, chiolite-based sodium aluminium fluoride compounds were used as pesticides and insecticides in agriculture for pest repellence, though this application has largely declined due to environmental and health concerns.

Benefits and Advantages of Chiolite:
The chiolite structural type (tetragonal, P4/mnc) is unique among sodium aluminium fluorides in that it contains both [AlF₆]³⁻ and [AlF₄]⁻ polyhedra in a single ordered framework, providing a structurally distinct fluoride melt modifier with a different AlF₃/NaF molar ratio from cryolite, enabling precise tuning of bath chemistry in aluminium electrolysis.
Synthetic chiolite is non-radioactive, chemically stable under normal operating conditions, and compatible with aluminium electrolysis bath materials; as a UVB phosphor host, the rigid tetragonal fluoride lattice provides a low-phonon energy environment that enhances lanthanide emission efficiency compared with oxide-based phosphor hosts.
Natural chiolite specimens from type locality Miask, Ivigtut (Greenland), and the Morefield Mine (Virginia) represent geologically irreplaceable reference materials for understanding fluoride pegmatite petrogenesis, fluoride mineral crystallochemistry, and the thermodynamic stability of the Na–Al–F system.
The extreme rarity of faceted chiolite — fewer than two dozen cut specimens globally — makes individual gemstone examples among the rarest collector items in the entire gem mineral world, holding both mineralogical provenance value and extreme scarcity premium.

Features of Chiolite:
Chiolite occurs as nearly colourless to snow-white massive or granular aggregates; distinct dipyramidal crystals with {111}, {001}, and {114} forms reaching up to 10 cm are rare; twinning on {011} may distort crystals into prismatic shapes; cleavage is perfect on {001} and distinct on {011}; luster is vitreous, pearly on cleavage faces, and sometimes greasy; streak is white; transparency is transparent to translucent.
Specific gravity is 2.998 (measured) / 2.989 (calculated) / 2.87 (electron density); Mohs hardness 2.5 (Pauly 1985 revised; historically reported as 3.5–4); Vickers hardness VHN₂₅ = 161 (122–206) on polished faces; chiolite is softer than cryolite (Mohs 2.5–3 for massive cryolite) and can be scratched by cryolite on its {001} cleavage face.
Optical properties: uniaxial negative; refractive indices nω = 1.3486, nε = 1.3424; birefringence 0.007; no pleochroism; no luminescence; not radioactive; photoelectric absorption PE = 1.19 barns/electron; unit cell a = 7.00–7.01 Å, c = 10.39–10.41 Å, Z = 2, unit cell volume 511.06 ų.
Composition: Na 24.89%, Al 17.53%, F 57.59% (theoretical); X-ray powder pattern principal lines: d = 2.91 Å (100%), 5.18 Å (80%), 2.32 Å (70%), 1.99 Å (70%), 1.79 Å (70%), 1.75 Å (70%), 1.55 Å (70%).

Mineralogical and Chemical Properties of Chiolite:
Chiolite belongs to the fluoride mineral class; the tetragonal structure (P4/mnc) contains a three-dimensional network of vertex-sharing [AlF₆]³⁻ octahedra and [AlF₄]⁻ tetrahedra linked by Na⁺ cations in the channels; the composition Na₅Al₃F₁₄ can be expressed as 3NaF·Na₂AlF₅·2AlF₃, with an AlF₃:NaF molar ratio of 3:5; it is structurally related to but distinct from cryolite (Na₃AlF₆, monoclinic, no cleavage).
The empirical formula Na₅Al₃F₁₄ is approved by the IMA (valid pre-IMA species, 1846); molecular weight 461.87 g/mol; exact mass 461.871106 Da; theoretical oxide composition: Na₂O 33.55%, Al₂O₃ 33.11%, F 57.59% (−O=F₂: −24.25%); Fermion index 0, Boson index 1; not radioactive.
Chiolite is chemically stable under normal conditions; it is soluble in water to a limited extent and dissolves in strong bases; it is hygroscopic under certain conditions; it decomposes in strong acids releasing HF; it is not flammable; compatible with aluminium electrolysis bath conditions up to approximately 700°C; incompatible with concentrated hydrofluoric acid and strong alkalis at elevated temperature.
When associated with topaz in pegmatites, brecciated chiolite transforms to cryolite along fragment rims by solid-state replacement, liberating aluminium and potassium; with silica addition, chiolite breakdown produces topaz and potassium mica; these solid-state mineralogical transformations are important indicators of late-stage pegmatite fluid evolution.

Occurrence and Production of Chiolite:
Chiolite forms exclusively in granite pegmatites under conditions of high fluorine activity during the late-magmatic to hydrothermal stages of pegmatite crystallisation; the narrow chemical window required for its stability (requiring both high F and appropriate Na/Al ratios) explains its exceptional rarity relative to associated cryolite.
The three principal gem-quality and specimen-quality localities are: Miask, Ilmen Mountains, Southern Ural Mountains, Russia (type locality; discovered 1846); Ivigtut cryolite deposit, Arsuk Fjord, southwestern Greenland (principal gem-quality source; first described here as arksutite); and Morefield pegmatite mine, Amelia County, Virginia, USA; additional occurrences include Brazil, Ukraine, and Norway.
Synthetic chiolite is manufactured for industrial use; production routes include reaction of NaF and AlF₃ in appropriate stoichiometric ratios (5:3) at elevated temperatures, or co-precipitation from sodium aluminium fluoride solutions; synthetic material is available at 99.9% purity (metals basis) for research and industrial applications; natural material is available as raw specimens, granular aggregates, and extremely rarely as faceted gems.

Chiolite Material Safety Data Sheet (MSDS):

Handling of Chiolite:
Chiolite dust contains fluoride and aluminium compounds; avoid inhalation of dust and vapours during processing, crushing, or heating operations; fluoride-containing dusts may cause respiratory irritation, and repeated or prolonged exposure to fluoride compounds may cause fluorosis.
Handle in a well-ventilated area; wear protective gloves, goggles, and a respirator where dust levels cannot be controlled; avoid contact with skin and eyes; do not eat, drink, or smoke during handling; wash hands thoroughly after handling.

Chiolite SDS:

Stability and Reactivity of Chiolite:

Chemical stability:
Chiolite is stable under recommended storage conditions in a dry, cool place in sealed containers. Chiolite is sensitive to moisture (hygroscopic under certain conditions) and to strong acids (liberates HF).

Reactivity:
Chiolite releases hydrogen fluoride (HF) in contact with concentrated mineral acids; at elevated temperatures, fluoride volatilisation may occur. Chiolite is not flammable and not explosive under normal conditions.

Conditions to avoid:
Contact with strong acids (HF liberation).
Prolonged moisture exposure (hygroscopic degradation).
Elevated temperatures >700°C in industrial processing.
Dust generation (fluoride dust inhalation hazard).

Incompatible materials:
Concentrated mineral acids (especially H₂SO₄ — liberates HF).
Strong alkalis at elevated temperature.
Oxidising agents (may promote fluoride volatilisation).

Hazardous decomposition products:
Hydrogen fluoride (HF) — on acid contact or at very high temperatures.
Aluminium oxide (Al₂O₃) and sodium fluoride (NaF) upon thermal decomposition.

Handling and Storage of Chiolite:

Handling:
Handle in well-ventilated areas; avoid dust generation.
Wear chemical-resistant gloves, safety goggles, and a respirator where dust cannot be controlled.
Avoid contact with skin and eyes; avoid inhalation.
Do not eat, drink, or smoke in work areas; wash hands after handling.

Storage:
Store in a dry, cool place in tightly sealed containers away from acids and moisture.
Natural specimens: no special requirements; store in dry conditions.
Synthetic industrial grade: store in sealed containers away from moisture.

First Aid Measures for Chiolite:

Inhalation:
Move the affected person to fresh air; if symptoms of fluoride irritation develop (coughing, chest tightness), consult a physician immediately.

Skin contact:
Wash with plenty of water; for prolonged exposure to fluoride dust, consult a physician.

Eye contact:
Rinse immediately with plenty of water for at least 15 minutes; consult a physician.

Ingestion:
Rinse the mouth with water; fluoride compounds may cause nausea and gastrointestinal irritation; consult a physician immediately; calcium gluconate may be indicated.

Firefighting Measures for Chiolite:

Suitable extinguishing media:
Chiolite is non-combustible; use extinguishing media appropriate to surrounding fire.

Specific hazards:
At very high temperatures, chiolite may release HF vapours and fluoride-containing fumes; these are corrosive and hazardous to the respiratory tract.

Protective equipment for firefighters:
SCBA and full protective clothing due to potential HF release at high temperatures.

Accidental Release Measures for Chiolite:

Personal precautions:
Avoid generating dust; wear respiratory protection if fine powder is present.

Environmental precautions:
Fluoride-containing minerals may leach fluoride into groundwater; prevent large quantities from entering water courses.

Clean-up methods:
Collect mechanically without generating dust; dispose in accordance with local regulations for fluoride-containing materials.

Exposure Controls / Personal Protective Equipment for Chiolite:

Engineering controls:
Local exhaust ventilation during grinding and processing of synthetic chiolite; wet processing preferred where possible.

Eye protection:
Chemical safety goggles.

Hand protection:
Chemical-resistant gloves (nitrile or neoprene).

Respiratory protection:
P95/P100 (US) or P2/P3 (EU EN 143) particulate filter for dusty operations; SCBA for high-temperature industrial operations with fluoride volatilisation risk.

Hygiene measures:
Wash hands before breaks and at end of workday; do not eat, drink, or smoke in work areas.

Chiolite Identifiers:
CAS Number: 1302-84-7
EC Number: 215-112-7
PubChem CID: 71300915
Alternate CAS: 12068-55-2 (synthetic grade, EINECS 237-410-6)
IMA Symbol: Cio
IMA Status: Valid Species (Pre-IMA) 1846
Strunz Classification: 03.CE.05
Dana Classification: 11.06.11.01
ICSD: 126419
RefChem: 125212
Mindat Occurrence Record ID: 3535
IUPAC Name: Pentasodium;bis(pentafluoroaluminum(2−));tetrafluoroalumanuide
Chemical Formula: Na₅Al₃F₁₄
Molecular Weight: 461.87 g/mol
Exact Mass: 461.871106 Da
Monoisotopic Mass: 461.871106 Da
SMILES: F[Al-](F)(F)F.F[Al-2](F)(F)(F)F.F[Al-2](F)(F)(F)F.[Na+].[Na+].[Na+].[Na+].[Na+]
InChI: InChI=1S/3Al.14FH.5Na/h;;;14*1H;;;;;/q3*+3;;;;;;;;;;;;;;;5*+1/p-14
InChIKey: PPPLOTGLKDTASM-UHFFFAOYSA-A
Heavy atom count: 22; HBA: 17; HBD: 0; Rotatable bonds: 0; Complexity: 56.2
Crystal System: Tetragonal
Crystal Class: Ditetragonal Dipyramidal 4/m 2/m 2/m
Space Group: P4/mnc
Unit Cell: a = 7.00–7.01 Å; c = 10.39–10.41 Å; Z = 2; V = 511.06 ų
GHS Classification: Not classified as hazardous (natural mineral); fluoride hazard applies to dust/heated material
Type Locality: Miask, Ilmen Mountains, Russia (1846)
Radioactivity: None

Properties of Chiolite:
Mineral class: Fluoride (halide mineral)
Chemical formula: Na₅Al₃F₁₄
Molecular weight: 461.87 g/mol
Composition: Na 24.89%, Al 17.53%, F 57.59%
Crystal system: Tetragonal
Crystal class: Ditetragonal dipyramidal (4/m 2/m 2/m)
Space group: P4/mnc
Colour: Nearly colourless; snow white; rarely pale grey or faintly bluish
Crystal habit: Mostly granular, massive; rarely dipyramidal crystals to 10 cm
Twinning: On {011}
Cleavage: {001} perfect; {011} distinct
Luster: Vitreous; pearly on cleavage; greasy
Streak: White
Transparency: Transparent to translucent
Mohs hardness: 2.5 (Pauly 1985); historically 3.5–4
VHN₂₅: 161 (122–206)
Specific gravity: 2.998 (measured); 2.989 (calculated)
Refractive index: nω = 1.3486; nε = 1.3424
Birefringence: 0.007
Optical character: Uniaxial (−)
Pleochroism: None
Luminescence: None
Radioactivity: None
GHS Classification: Not classified (bulk natural mineral)
Storage: Dry, sealed containers

Chiolite Properties — Specifications:
Product name: Chiolite (Na₅Al₃F₁₄)
CAS Number: 1302-84-7
EC Number: 215-112-7
IMA Symbol: Cio
Chemical Formula: Na₅Al₃F₁₄
Molecular Weight: 461.87 g/mol
Purity (synthetic): 99.9% (metals basis)
Appearance: White to colourless crystalline solid or powder
Specific gravity: 2.998
Mohs hardness: 2.5
Storage: Dry, sealed containers, away from moisture and acids
Format: Natural specimens (mineralogical); granular/powder (industrial); faceted gem (extremely rare collector)
Documents: Product data sheet, CoA available for synthetic grades on request

Names of Chiolite:
Chiolite
Chiolithe
Arksutite
Arksudite
Chodneffite
Chodnewite
Nipholith
Sodium aluminium fluoride
Na₅Al₃F₁₄
Al₃F₁₄Na₅
Pentasodium tris(tetrafluoroaluminate)
IMA symbol Cio
CAS 1302-84-7
EINECS 215-112-7
PubChem CID 71300915
ICSD 126419