Calcium fluoride

Ca 1
F 2

Formula unit Lattice

Choose Lattice to see one unit cell. Then drag to rotate; pinch or Ctrl + scroll to zoom. Arrow keys rotate, + − zoom, R resets.

3 atoms in one formula unit of an ionic lattice.

The drawing shows one formula unit of an ionic lattice, not a molecule; calcium fluoride has no molecular shape.

IUPAC name: calcium difluoride
Molar mass: 78.0740(60) g/mol
Atoms: 3
SMILES: [F-].[F-].[Ca+2]
InChIKey: WUKWITHWXAAZEY-UHFFFAOYSA-L
PubChem CID: 84512

Made of

Ca F

Much of the fluorine that industry handles starts out as calcium fluoride, which Haz-Map names as the chief source of fluorine and fluorine compounds. In nature it is the mineral fluorite, also called fluorspar, which Los Alamos describes as forming regular crystals. Each formula unit pairs one calcium ion, Ca²⁺, with two fluoride ions, F⁻, the ratio that the IUPAC name, calcium difluoride, spells out.

The International Chemical Safety Cards describe the solid as colourless crystals or a white hygroscopic powder, one that takes up moisture from the air. Very little of it dissolves in water: 0.0017 g in 100 g at 25 °C, on the figure of HSDB, the Hazardous Substances Data Bank. In water that already holds calcium or fluoride ions from another salt, even less dissolves. Chem1 names this the common-ion effect, a marked drop in the solubility of a sparingly soluble ionic solid.

Structure and bonding

One calcium ion, charge +2, and two fluoride ions, charge −1 each, appear in the drawing as three separate pieces with no bonds between them. Together they make one formula unit of the crystal, the ratio of its ions rather than a separate particle. The attraction that holds such ions in place is explained in the article on chemical bonding.

Switched to Lattice, the model becomes one unit cell, the block that repeats in three dimensions to build the crystal. It holds 4 calcium ions and 8 fluoride ions. Each calcium ion sits among 8 fluoride ions, and each fluoride ion among 4 calcium ions, 2.37 Å away. With Coordination on, the model picks out one fluoride ion and its 4 nearest neighbours.

In fluorite, on Chem1’s account, the calcium ions take a cubic close-packed arrangement, a way of stacking equal spheres as tightly as they go, also called face-centred cubic. Fluoride ions occupy every one of its tetrahedral holes, gaps whose four surrounding ions mark the corners of a tetrahedron. Ions too large for such holes push the host ions apart, though, and in calcium fluoride their sizes rule out true close packing.

Where it turns up

Pure calcium fluoride has no colour, yet HSDB describes natural fluorite ranging from clear and white through wine-yellow, green and violet-blue to deep purple, bluish black and brown. The National Park Service counts it among the world’s most colourful minerals. Under ultraviolet light the mineral glows, and fluorescence takes its name from it. At 4 on the Mohs scale of hardness it is softer than quartz, for which it is often mistaken.

Illinois, once the top US producer according to the National Park Service, has fluorite as its state mineral. The United States produced minimal fluorspar in 2024. One company sold from stockpiles left over from limestone quarrying at Cave-In-Rock, Illinois, and imports satisfied US consumption. World production reached an estimated 9.5 million tons that year, 5.9 million of them from China, the US Geological Survey reports.

Why it matters

Fluorine’s name comes from a job calcium fluoride has done for centuries. CIAAW, IUPAC’s atomic-weights commission, traces it to the Latin fluere, “to flow”, because fluorite served metallurgy as a flux, an additive helping melts flow, thanks to its low melting point. Agricola described fluorspar’s use as a flux in 1529. Steelmakers still add it as a flux today, one that makes the slag, the molten waste on the metal, more fluid, in HSDB’s account.

Synthetic crystals take calcium fluoride into optics, where it is used because it transmits ultraviolet rays (HSDB). In chip-making, photolithography exposes a mask to ultraviolet light in machines called steppers. At 193 nm their lenses were usually fused silica, the US standards agency NIST reported in 2003, while proposed 157 nm steppers for finer features would use calcium fluoride.

The crystals also make lenses that focus infrared light, Jefferson Lab notes. NASA’s Europa Clipper carries one in an instrument that gathers infrared light reflected from Europa. Its calcium fluoride lens directs the light onto a diffraction grating, which spreads it into separate wavelengths.

Properties

Properties of calcium fluoride Molar mass summed from IUPAC/CIAAW 2024 standard atomic weights; formula, atom and bond counts and PubChem's molecular weight from PubChem CID 84512.
Property	Value	Unit	Source
Formula (Hill order)	CaF₂
Molar mass	78.0740(60) g/mol	g/mol	IUPAC/CIAAW 2024
Calcium atoms	1
Fluorine atoms	2
PubChem molecular weight	78.07 g/mol	g/mol	PubChem

Safety

Calcium fluoride can irritate the skin, the eyes and the airways. Those are the hazards that 48.2% of 955 reports to the European Chemicals Agency classify under the Globally Harmonized System (GHS); 51.7% find none. Heated to decomposition, it gives off toxic fumes of hydrogen fluoride. Workplace exposure limits exist for fluorides, and the PubChem Laboratory Chemical Safety Summary for calcium fluoride collects them with these classifications.

Questions

Why does calcium fluoride have twice as many fluoride ions as calcium ions?

The charges set the ratio: each calcium ion carries +2 and each fluoride ion −1, so two fluoride ions balance one calcium ion. The crystal's geometry shows the same ratio. In the Lattice view each calcium ion has eight fluoride neighbours while each fluoride ion has only four calcium neighbours, and one unit cell holds 4 calcium ions against 8 fluoride ions.

Is calcium fluoride the fluoride in drinking water and toothpaste?

Pure calcium fluoride is used to fluoridate drinking water, according to MeSH, the US National Library of Medicine's subject vocabulary. The compounds commonly added, says ATSDR, the US Agency for Toxic Substances and Disease Registry, are sodium fluoride, fluorosilicic acid and sodium fluorosilicate. Sodium fluoride dissolves easily in water and calcium fluoride does not, ATSDR adds. HSDB lists dentifrices, that is toothpastes and tooth powders, among the uses of fluorspar.

What is calcium fluoride used for?

The steel, chemical, ceramics and glass industries use it, according to Haz-Map, and the US Geological Survey adds cement, enamels, iron and steel casting and welding-rod coatings. Mined fluorspar is concentrated into three grades: metallurgical, ceramic at 85 to 97 per cent calcium fluoride, and acid at more than 97 per cent (HSDB). MeSH lists the pure compound as a catalyst for dehydration and dehydrogenation, reactions that strip water or hydrogen from a molecule.

Is calcium fluoride toxic?

Its acute toxicity is low, on the assessment of CAMEO Chemicals. ACGIH, the American Conference of Governmental Industrial Hygienists, places fluorides as a group in category A4, not classifiable as a human carcinogen. Calcium fluoride does not burn, and it reacts rapidly with neither air nor water. The hazards classified for it are irritant ones, and the PubChem Laboratory Chemical Safety Summary for calcium fluoride gathers them.