Calcium Fluoride
Properties
| State | Solid (crystalline) |
| Color | Colorless to white (pure); various colors as mineral fluorite |
| Solubility | Practically insoluble in water (0.016 g/L at 18°C) |
| Melting Point | 1418°C |
| Boiling Point | 2533°C |
About Calcium Fluoride
Calcium fluoride is the structural archetype that defined a whole class of crystallography — the fluorite structure, in which Ca²⁺ ions occupy a face-centered cubic lattice and F⁻ ions fill all the tetrahedral holes, giving every Ca²⁺ an eight-coordinate cubic environment and every F⁻ a tetrahedral one. UO2, ZrO2, and ThO2 all share this packing, and 'fluorite-type' is now a textbook label. Two properties dominate its industrial life. First, it is the world's primary fluorine reservoir: treat fluorspar with concentrated H2SO4 in a heated rotary kiln and you get CaF2 + H2SO4 → CaSO4 + 2 HF, and that anhydrous HF is the feedstock for refrigerants, fluoropolymers like PTFE, fluorinated pharmaceuticals (the C–F bond appears in roughly a quarter of all small-molecule drugs, including atorvastatin and fluoxetine), and uranium hexafluoride for enrichment. Second, single-crystal CaF2 transmits cleanly from about 130 nm in the deep UV out to 10 µm in the IR, with a refractive index near 1.43 and almost no chromatic dispersion across that window — properties that have made it the standard window material for FTIR cells, excimer-laser optics at 193 nm, and corrected lens elements in semiconductor photolithography. Its solubility product Ksp ≈ 3.45 × 10⁻¹¹ also makes it the canonical worked example for solubility equilibrium in any general chemistry textbook.
Where you'll encounter it
If you have ever loaded a sample into an FTIR with CaF2 windows, you have handled the same material that comes out of fluorite mines in Mexico, China, and Mongolia. Steelmakers have a different relationship with it — fluorspar is dumped into the basic oxygen furnace at about 0.5% of the iron charge to fluidize the slag and let phosphorus and sulfur partition out of the metal. Mineral collectors prize fluorite for the dramatic purple, green, and yellow cubes it grows in hydrothermal veins (the colors come from F-center defects and trace REE substitution, not from any chromophoric impurity). And every F-containing pharmaceutical — Lipitor, Prozac, Cipro, the entire fluoroquinolone class — traces its fluorine atoms back through the HF synthesis chain to a sulfuric-acid attack on a chunk of CaF2.
Common Uses
- Feedstock for anhydrous HF via the H2SO4 attack route, the gateway to all fluorine chemistry
- Fluidizing flux in basic oxygen steelmaking at roughly 0.5% of charge
- Single-crystal windows and lenses for VUV (193 nm) and broadband IR optics
- Standard window material for FTIR transmission cells in aqueous samples
- Apochromatic and fluorite-doublet lens elements in microscopy and astrophotography
- Worked example for Ksp calculations in undergraduate equilibrium courses
- Component in Welsbach gas-mantle thoria and in some optical-glass formulations
Safety Information
Solid CaF2 is barely toxic on its own — Ksp is so low that almost no F⁻ goes into solution at neutral pH, and oral exposure to dust is bounded by the same insolubility. The serious hazard is what happens when CaF2 meets a strong acid: it liberates HF, which is the most insidious acid in any lab. HF causes deep-tissue burns that may not show pain for hours, and systemic Ca²⁺ chelation can cause cardiac arrhythmia. Airborne HF limits are set far below those for common mineral acid vapors. Treat any acid-spill scenario near fluorite stockpiles with calcium gluconate gel on hand and full PPE.
This safety summary is for educational reference only and may not be complete. It is not a substitute for Safety Data Sheets (SDS), medical advice, or professional chemical safety guidance. Always consult appropriate SDS and qualified professionals before handling chemicals. We deliberately do not publish occupational exposure limits or other regulatory thresholds: those values are revised over time and differ between jurisdictions, so the only correct source is the current SDS and the regulations that apply where you work.