spore: profile
id: calcium-fluoride
spore_version: 0.2
family: optical-crystals
name: Calcium fluoride (single-crystal CaF2, fluorite)
abbreviation: CaF2
role: UV and IR optical crystal for windows, lenses and prisms
category: glasses-optics
type: optical-crystals
summary: |
  Calcium fluoride is the fluorite-structure crystal CaF2, grown by the vacuum Stockbarger method in diameters up to about 250 mm. Crystran gives a transmission range of 0.13 to 10 µm, a refractive index of 1.39908 at 5 µm and a density of 3.18 g/cc, and it says the UV grades use chemically prepared raw material while the IR grade uses naturally mined fluorite. Barium fluoride transmits to 12 µm and magnesium fluoride reaches the hydrogen Lyman-alpha line at 121 nm; both are compared briefly below. The sources read give no ground radiation test or orbital result for calcium fluoride.
best_for: Windows, lenses and prisms that must pass light from the vacuum ultraviolet to the infrared, including excimer-laser optics and Raman spectroscopy (Crystran)
weakest_at: 'Brittleness: the crystal cleaves on the (111) plane, and it reacts with strong mineral acids to give hydrogen fluoride gas (Crystran)'
identity:
  formula: CaF2
  cas: 7789-75-5
  crystal_system: cubic
  space_group: Fm3m (#225), fluorite structure
  designations:
    - system: Trade name
      code: Irtran-3
      source: crystran-caf2-msds
      where: Section 1.1, Synonyms and trade names
  source: crystran-caf2-datasheet
  where: Class/Structure row (Cubic Fm3m (#225) Fluorite structure, cleaves on (111)); CAS 7789-75-5 from crystran-caf2-msds section 3.1; molecular weight 78.08 on the Crystran sheet and 78.07 for CID 24617 from PubChem
tags:
  environments: []
  stresses: []
  applications:
    - optics-and-cameras
properties:
  - benchmark: refractive_index
    label: Refractive index at 5 µm
    value: 1.39908
    unit: '-'
    scope: material
    conditions:
      wavelength: 5 µm
    method: Value printed on a manufacturer materials data sheet (from Palik and Dressler references); the same sheet prints a reflection loss of 5.4% at 5 µm
    status: ground
    source: crystran-caf2-datasheet
    where: Data table, Refractive Index row (1.39908 at 5µm)
  - benchmark: density
    label: Density
    value: 3.18
    unit: g/cc
    scope: material
    conditions:
      temperature: not stated on the page
    method: Value printed on a manufacturer materials data sheet
    status: ground
    source: crystran-caf2-datasheet
    where: Data table, Density row
  - benchmark: melting_point
    label: Melting point
    value: 1360
    unit: °C
    scope: material
    conditions:
      form: single crystal
    method: Value printed on a manufacturer materials data sheet; the safety sheet prints the same 1360 C
    status: ground
    source: crystran-caf2-datasheet
    where: Data table, Melting Point row
  - benchmark: boiling_point
    label: Boiling point, approximate
    value: 2500
    unit: °C
    scope: material
    conditions:
      pressure: 760 mmHg
    method: Printed as an approximate value (about 2500 C) in a safety data sheet
    status: ground
    note: The sheet prints the value with a tilde, so it is approximate.
    source: crystran-caf2-msds
    where: Section 9.1, BOILING POINT row
  - benchmark: thermal_conductivity
    label: Thermal conductivity
    value: 9.71
    unit: W/(m·K)
    scope: material
    conditions:
      temperature: not stated on the page
    method: Value printed on a manufacturer materials data sheet (from Ballard et al., 1950, reference 4)
    status: ground
    source: crystran-caf2-datasheet
    where: Data table, Thermal Conductivity row
  - benchmark: cte
    label: Coefficient of thermal expansion
    value: 18.85
    unit: ppm/K
    scope: material
    conditions:
      unit_in_source: 10^-6 K^-1
      temperature: not stated on the page
    method: Printed as 18.85 x 10^-6 K^-1, which is the same as ppm/K; no conversion of the number
    status: ground
    source: crystran-caf2-datasheet
    where: Data table, Thermal Expansion row
  - benchmark: specific_heat
    label: Specific heat capacity
    value: 854
    unit: J/(kg·K)
    scope: material
    conditions:
      temperature: not stated on the page
    method: Value printed on a manufacturer materials data sheet
    status: ground
    source: crystran-caf2-datasheet
    where: Data table, Specific Heat Capacity row
  - benchmark: dielectric_constant
    label: Dielectric constant at 1 MHz
    value: 6.76
    unit: '-'
    scope: material
    conditions:
      frequency: 1 MHz
    method: Value printed on a manufacturer materials data sheet (reference 7, Dickinson 1975)
    status: ground
    source: crystran-caf2-datasheet
    where: Data table, Dielectric Constant row
  - benchmark: elastic_modulus
    label: Young's modulus
    value: 75.8
    unit: GPa
    scope: material
    conditions:
      temperature: not stated on the page
    method: Value printed on a manufacturer materials data sheet (reference 7, Dickinson 1975)
    status: ground
    source: crystran-caf2-datasheet
    where: Data table, Youngs Modulus (E) row
  - benchmark: shear_modulus
    label: Shear modulus
    value: 33.77
    unit: GPa
    scope: material
    conditions:
      temperature: not stated on the page
    method: Value printed on a manufacturer materials data sheet (reference 7)
    status: ground
    source: crystran-caf2-datasheet
    where: Data table, Shear Modulus (G) row
  - benchmark: bulk_modulus
    label: Bulk modulus
    value: 82.71
    unit: GPa
    scope: material
    conditions:
      temperature: not stated on the page
    method: Value printed on a manufacturer materials data sheet (reference 7)
    status: ground
    source: crystran-caf2-datasheet
    where: Data table, Bulk Modulus (K) row
  - benchmark: poissons_ratio
    label: Poisson ratio
    value: 0.26
    unit: '-'
    scope: material
    conditions:
      temperature: not stated on the page
    method: Value printed on a manufacturer materials data sheet
    status: ground
    source: crystran-caf2-datasheet
    where: Data table, Poisson Ratio row
  - benchmark: apparent_elastic_limit
    label: Apparent elastic limit
    value: 36.54
    unit: MPa
    scope: material
    conditions:
      temperature: not stated on the page
    method: Value printed on a manufacturer materials data sheet; not a canonical property name
    status: ground
    source: crystran-caf2-datasheet
    where: Data table, Apparent Elastic Limit row
  - benchmark: reststrahlen_peak
    label: Reststrahlen peak
    value: 35
    unit: µm
    scope: material
    conditions:
      temperature: not stated on the page
    method: Value printed on a manufacturer materials data sheet; not a canonical property name
    status: ground
    source: crystran-caf2-datasheet
    where: Data table, Reststrahlen Peak row
  - benchmark: transmission_range
    label: Transmission range
    value: 0.13
    value_high: 10
    bound: range
    unit: µm
    scope: material
    conditions:
      thickness: not stated on the page
    method: Range printed on a manufacturer materials data sheet; not a canonical property name
    status: ground
    note: The datasheet shows transmission curves for 0.5 to 10 mm thick samples and a VUV trace for specially qualified material; the range is taken from the data table, not the curves.
    source: crystran-caf2-datasheet
    where: Data table, Transmission Range row
  - benchmark: refractive_index_temperature_coefficient
    label: Refractive index change with temperature (dn/dT)
    value: -10.6
    unit: ppm/K
    scope: material
    conditions:
      unit_in_source: 10^-6 K^-1
      wavelength: not stated on the page
    method: Printed as -10.6 x 10^-6 K^-1 with reference 3 (Malitson 1962); not a canonical property name
    status: ground
    source: crystran-caf2-datasheet
    where: Data table, dn/dT row
  - benchmark: water_solubility
    label: Solubility in water at 20 °C
    value: 0.0017
    unit: g/100 g water
    scope: material
    conditions:
      temperature: 20 °C
    method: Value printed on a manufacturer materials data sheet; not a canonical property name
    status: ground
    source: crystran-caf2-datasheet
    where: Data table, Solubility row
corrosion:
  - environment: Strong mineral acids
    headline: Calcium fluoride reacts with strong mineral acids and gives off hydrogen fluoride gas.
    effect: The Crystran safety sheet lists strong mineral acids as incompatible and says that the decomposition product is hydrogen fluoride gas. No rate or concentration is printed, so the rating is qualitative.
    rating: moderate
    conditions:
      basis: qualitative reactivity statement; no rate or concentration printed
      agent: strong mineral acids
    source: crystran-caf2-msds
    where: Sections 10.1, 10.5 and 10.6
  - environment: Water at 20 °C
    headline: Calcium fluoride is practically insoluble in water.
    effect: The data sheet gives a solubility of 0.0017 g per 100 g of water at 20 C, and the safety sheet calls the material practically insoluble. No dissolution or corrosion test is printed.
    rating: low
    conditions:
      temperature: 20 °C
      note: solubility figure, not a corrosion rate
    source: crystran-caf2-datasheet
    where: Data table, Solubility row; crystran-caf2-msds section 9.1
  - environment: Water at 23 °C, barium fluoride (for comparison)
    headline: Barium fluoride is slightly soluble in water.
    effect: The barium fluoride data sheet gives a solubility of 0.17 g per 100 g of water at 23 C, which is about a hundred times the calcium fluoride figure. No dissolution test is printed.
    rating: low
    conditions:
      temperature: 23 °C
      note: solubility figure, not a corrosion rate
    source: crystran-baf2-datasheet
    where: Data table, Solubility row
  - environment: Water, magnesium fluoride (for comparison)
    headline: Magnesium fluoride is practically insoluble in water.
    effect: The magnesium fluoride data sheet gives a solubility of 0.0002 g per 100 g of water, and the safety sheet calls it practically insoluble. No corrosion test is printed.
    rating: low
    conditions:
      note: solubility figure, not a corrosion rate; temperature not stated
    source: crystran-mgf2-datasheet
    where: Data table, Solubility row; crystran-mgf2-msds section 9.1
risks:
  hazards:
    - text: The Crystran safety sheet (revision 2026) gives H315 (causes skin irritation), H319 (causes serious eye irritation) and H332 (harmful if inhaled), with the signal word Warning. It says the product is harmful in contact with skin and eyes, and it advises particular care when machining and when dust or particles form.
      ghs:
        - H315
        - H319
        - H332
      source: crystran-caf2-msds
      where: Sections 2.1 and 2.2
    - text: The same sheet says the material is toxic by ingestion and by inhalation of dust, with a cumulative effect, and that it affects the nervous system. It gives an oral LD50 above 4250 mg/kg in rats, and says there is no evidence of carcinogenic properties.
      ghs: []
      source: crystran-caf2-msds
      where: Section 11.1
    - text: The sheet gives an occupational exposure limit of 2.5 mg/m3 long term, expressed as fluoride (F), and says to avoid making dust.
      ghs: []
      source: crystran-caf2-msds
      where: Sections 8.1 and 6.1
    - text: The barium fluoride safety sheet (Crystran, revision 2015) classes the material as a class 6.1 poison, with H302 (harmful if swallowed), H315, H319 and H332. It gives an oral LD50 above 50 mg/kg in rats and an occupational limit of 0.5 mg/m3 as barium.
      ghs:
        - H302
        - H315
        - H319
        - H332
      source: crystran-baf2-msds
      where: Sections 2.1, 2.2, 8.1 and 11.1
    - text: The magnesium fluoride safety sheet (Crystran, revision 2026) gives H315, H319 and H332, with an oral LD50 above 2330 mg/kg in rats and an occupational limit of 2.5 mg/m3 long term as fluoride.
      ghs:
        - H315
        - H319
        - H332
      source: crystran-mgf2-msds
      where: Sections 2.2, 8.1 and 11.1
  failure_risks:
    - mode: Cleavage on the (111) plane
      trigger: Impact or mechanical stress on a crystal or a polished piece
      consequence: The data sheet says calcium fluoride cleaves on (111), so a piece can split along a crystal plane rather than break cleanly. The apparent elastic limit is printed as 36.54 MPa.
      severity: moderate
      source: crystran-caf2-datasheet
      where: Class/Structure row; Apparent Elastic Limit row
    - mode: Thermal shock (barium fluoride)
      trigger: Rapid temperature change of a barium fluoride piece
      consequence: The barium fluoride data sheet says the material cleaves easily and is highly susceptible to thermal shock. The calcium fluoride sheet gives no thermal shock figure.
      severity: high
      source: crystran-baf2-datasheet
      where: Introduction text, first paragraph
    - mode: Slight birefringence (magnesium fluoride)
      trigger: Use of a magnesium fluoride window with its optic axis at an angle to the faces
      consequence: The magnesium fluoride sheet says the material is slightly birefringent and is usually supplied with the optic axis normal to the faces. A window cut in another direction would change light polarisation.
      severity: low
      source: crystran-mgf2-datasheet
      where: Introduction text, first paragraph
  side_effects: []
  handling:
    - text: Wear PVA gloves, a laboratory coat and safety goggles or glasses where chipping or dust may occur. Provide mechanical and local exhaust ventilation, and wash hands after handling.
      source: crystran-caf2-msds
      where: Section 8, Exposure controls
    - text: Avoid making dust. Take up broken pieces into containers for disposal, and avoid sharp edges.
      source: crystran-caf2-msds
      where: Sections 6.1 and 6.3
    - text: Keep away from heat, strong acids and foodstuffs, and protect the crystal from physical damage.
      source: crystran-caf2-msds
      where: Sections 7.1 and 7.2
  mitigations:
    - text: Specify the optic-axis orientation for magnesium fluoride windows. The Crystran sheet says the usual cut has the optic axis perpendicular to the faces.
      source: crystran-mgf2-datasheet
      where: Introduction text, first paragraph
uses:
  - application: optics-and-cameras
    device: Infrared spectroscopic windows, prisms and lenses
    example: Crystran lists calcium fluoride for IR spectroscopic windows, prisms and lenses, and says selected grades are used for Raman work because the material has no interfering fluorescence peaks.
    source: crystran-caf2-datasheet
    where: Applications text, first paragraph
  - application: optics-and-cameras
    device: Excimer laser windows and UV optics
    example: Crystran says the highest-purity grades are used in the UV and as excimer laser windows. Its UV grades use chemically prepared raw material.
    source: crystran-caf2-datasheet
    where: Materials data text, first paragraph
  - application: optics-and-cameras
    device: Lithography optics at 193 nm and 157 nm
    example: A 2000 NIST review of optical materials for 193 nm and 157 nm lithography covers calcium fluoride, with representative index values near 157 nm. The abstract does not print the numbers.
    source: nist-burnett-gupta-2000
    where: Abstract
  - application: optics-and-cameras
    device: Hydrogen Lyman-alpha optics (magnesium fluoride)
    example: Crystran says magnesium fluoride transmits well into the VUV to the hydrogen Lyman-alpha line at 121 nm and beyond, and is used mostly for UV optics and excimer laser work.
    source: crystran-mgf2-datasheet
    where: Applications text, first paragraph
  - application: optics-and-cameras
    device: Thermography view-port windows (barium fluoride)
    example: Crystran says barium fluoride is often used as a view-port window for thermography in the 8 to 14 µm band, and that its highest-purity grade is a fast scintillator used in high-energy physics experiments.
    source: crystran-baf2-datasheet
    where: Applications text, first paragraph
supply:
  - subject: Fluorspar, the mineral form of calcium fluoride (world mine production, 2025 estimate)
    producers:
      - country: China
        share_percent: 60
        year: 2025
      - country: Mexico
        share_percent: 15
        year: 2025
      - country: Mongolia
        share_percent: 15
        year: 2025
      - country: South Africa
        share_percent: 4.1
        year: 2025
    critical_lists:
      - list: USGS 2025 List of Critical Minerals (fluorspar, as summarised in CRS report IF13145)
        listed: true
    recycling: 'USGS: synthetic fluorspar may be produced from waste neutralisation in uranium enrichment, petroleum alkylation and stainless-steel pickling, but undesirable impurities constrain its use. Primary aluminium producers recycle HF and fluorides from smelting.'
    substitutes:
      - 'USGS: fluosilicic acid (FSA) is an alternative to fluorspar in making AlF3 and HF, and aluminium smelting dross, borax, calcium chloride, iron oxides, manganese ore, silica sand and titanium dioxide substitute for fluorspar fluxes. The chapter does not discuss optical-grade crystal.'
    source: usgs-mcs2026-fluorspar
    where: 'World Mine Production and Reserves table, 2025 column (China 6,000, Mexico 1,500, Mongolia 1,500, South Africa 410 of a world total of 10,000 thousand tons). Shares calculated by Space Mushroom as country value divided by the printed world total. Reserves column: China 110,000 and world total 330,000 thousand tons. Recycling, Substitutes and Critical lists sections.'
  - subject: US fluorspar import sources (2021 to 2024, as printed)
    producers:
      - country: Mexico
        share_percent: 64
        year: 2024
      - country: Vietnam
        share_percent: 12
        year: 2024
      - country: China
        share_percent: 10
        year: 2024
      - country: South Africa
        share_percent: 9
        year: 2024
    critical_lists: []
    recycling: Not repeated here; see the first supply entry.
    substitutes: []
    source: usgs-mcs2026-fluorspar
    where: Import Sources (2021 to 2024) line, printed as Mexico 64 percent, Vietnam 12, China 10, South Africa 9 and other 5. The year shown is the last year of the range.
documents:
  - title: 'Crystran: Calcium Fluoride (CaF2) materials data sheet (undated PDF, data table and refractive index table)'
    type: datasheet
    url: https://www.crystran.com/wp-content/uploads/2025/09/calcium-fluoride-caf2-data-sheet.pdf
    year: 2026
  - title: 'Crystran: Safety Data Sheet, Calcium Fluoride Optical Crystal (revision 2026, issued 6 July 2026)'
    type: sds
    url: https://www.crystran.com/wp-content/uploads/2025/09/calcium-fluoride-caf2-msds.pdf
    year: 2026
  - title: 'Crystran: Barium Fluoride (BaF2) materials data sheet (undated PDF)'
    type: datasheet
    url: https://www.crystran.com/wp-content/uploads/2025/09/barium-fluoride-baf2-data-sheet.pdf
    year: 2026
  - title: 'Crystran: Safety Data Sheet, Barium Fluoride (revision 2015, issued 9 September 2015)'
    type: sds
    url: https://www.crystran.com/wp-content/uploads/2025/09/barium-fluoride-baf2-msds.pdf
    year: 2015
  - title: 'Crystran: Magnesium Fluoride (MgF2) materials data sheet (undated PDF)'
    type: datasheet
    url: https://www.crystran.com/wp-content/uploads/2025/09/magnesium-fluoride-mgf2-data-sheet.pdf
    year: 2026
  - title: 'Crystran: Safety Data Sheet, Magnesium Fluoride (revision 2026, issued 6 July 2026)'
    type: sds
    url: https://www.crystran.com/wp-content/uploads/2025/09/magnesium-fluoride-mgf2-msds.pdf
    year: 2026
  - title: 'USGS Mineral Commodity Summaries 2026: Fluorspar'
    type: report
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-fluorspar.pdf
    year: 2026
  - title: 'NIST: Burnett and Gupta, Optical Materials and Detector Characterization for 193 nm and 157 nm Lithography (Future Fab International 8, 2000)'
    type: paper
    url: https://www.nist.gov/node/728211
    year: 2000
  - title: 'PubChem: Fluorite, calcium fluoride (CID 24617), compound record'
    type: database
    url: https://pubchem.ncbi.nlm.nih.gov/compound/24617
    year: 2026
  - title: 'Congressional Research Service: U.S. Geological Survey''s Critical Minerals List (IF13145)'
    type: report
    url: https://www.everycrsreport.com/reports/IF13145.html
    year: 2026
gaps:
  - No ground or orbital radiation test, UV ageing result, outgassing (TML/CVCM) or atomic-oxygen result for calcium fluoride was found in a source we could open. The 1981 NASA glass radiation report that the sapphire profile uses contains no fluoride results.
  - A synchrotron study comparing MgF2, CaF2, BaF2, fused silica and sapphire under UV damage was seen only as a search summary. The article page could not be opened (bot check), so it is not used.
  - 'Knoop hardness is not entered: Crystran prints 158.3 for calcium fluoride, 82 for barium fluoride and 415 for magnesium fluoride, all without a unit.'
  - Magnesium fluoride dn/dT (2.3 parallel and 1.7 perpendicular at 0.4 µm) is printed without a unit, so it is not entered.
  - 'Five benchmark names are not in the canonical list and are kept as snake_case: apparent_elastic_limit, reststrahlen_peak, transmission_range, refractive_index_temperature_coefficient and water_solubility.'
  - 'The PubChem GHS summary for CID 24617 could not be read: the public page shows a bot check, and the REST record holds no GHS text. Hazard data come from the Crystran safety sheets, which are supplier documents and cover only the Crystran grade.'
  - Only one supplier's safety sheet was read for each fluoride. Other supplier sheets seen in search results give different hazard statements (for example H335), but they were not opened and are not used.
  - 'Melting point differs between sheets: barium fluoride 1386 C on the 2026 data sheet and 1355 C on the 2015 safety sheet; magnesium fluoride 1255 C on the data sheet and 1248 C on the 2026 safety sheet. The data sheet value is used in each case.'
  - Thermal conductivity and thermal expansion for calcium fluoride are not given with a temperature on the data sheet.
  - The calcium fluoride transmission curves and the VUV trace are not read as numbers; the range is from the data table only.
  - Magnesium fluoride and barium fluoride are covered briefly in the story and the uses. Their full property sets are not in this file, which is written for calcium fluoride.
  - No production or country data was found for magnesium fluoride or for optical-grade calcium fluoride crystal. Supply shares are for fluorspar, the feedstock, and not for crystal output.
  - The critical-mineral status of fluorspar comes from a Congressional Research Service summary of the USGS 2025 list, not from the USGS list itself.
  - 'Sister fluorides, figures printed on their own Crystran sheets and not entered as properties of this profile: barium fluoride transmits 0.15 to 12 µm, has a density of 4.89 g/cc and a melting point of 1386 C on its 2026 data sheet, and dissolves 0.17 g per 100 g of water at 23 C; magnesium fluoride transmits 0.12 to 7 µm, has a density of 3.1766 g/cc and a melting point of 1255 C on its data sheet, and the 2026 safety sheet prints 1248 C for the same material.'
  - No media (photograph or drawing with a licence) was checked for this profile.
license: CC-BY-4.0
updated: '2026-10-26'
review:
  status: draft
  method: assistant
  checked_values: 17
  unreachable: 1
  caveats: 4
  note: 'Written by an AI assistant on 2026-10-26 from supplier data sheets, safety sheets and USGS and NIST pages read in the same run. Caveats: the PubChem hazard summary could not be read; the BESSY radiation study could not be opened; magnesium fluoride and barium fluoride are covered briefly; the Crystran sheets for calcium fluoride carry no publication date.'
sources:
  crystran-caf2-datasheet:
    title: 'Crystran: Calcium Fluoride (CaF2) materials data sheet (data table, refractive index table, VUV trace)'
    id: calcium-fluoride-caf2-data-sheet.pdf (undated; pages 48 and 49)
    url: https://www.crystran.com/wp-content/uploads/2025/09/calcium-fluoride-caf2-data-sheet.pdf
    year: 2026
    kind: datasheet
    license: supplier document, linked not reproduced
  crystran-caf2-msds:
    title: 'Crystran: Safety Data Sheet, Calcium Fluoride Optical Crystal (REACH format, revision 2026)'
    id: Revision 2026, issued 6 July 2026; CAS 7789-75-5; EC 232-188-7
    url: https://www.crystran.com/wp-content/uploads/2025/09/calcium-fluoride-caf2-msds.pdf
    year: 2026
    kind: datasheet
    license: supplier document, linked not reproduced
  crystran-baf2-datasheet:
    title: 'Crystran: Barium Fluoride (BaF2) materials data sheet'
    id: barium-fluoride-baf2-data-sheet.pdf (undated; page 38)
    url: https://www.crystran.com/wp-content/uploads/2025/09/barium-fluoride-baf2-data-sheet.pdf
    year: 2026
    kind: datasheet
    license: supplier document, linked not reproduced
  crystran-baf2-msds:
    title: 'Crystran: Safety Data Sheet, Barium Fluoride (revision 2015)'
    id: Revision 2015, issued 9 September 2015; CAS 7787-32-8; EC 232-108-0
    url: https://www.crystran.com/wp-content/uploads/2025/09/barium-fluoride-baf2-msds.pdf
    year: 2015
    kind: datasheet
    license: supplier document, linked not reproduced
  crystran-mgf2-datasheet:
    title: 'Crystran: Magnesium Fluoride (MgF2) materials data sheet (data table, refractive index table)'
    id: magnesium-fluoride-mgf2-data-sheet.pdf (undated; pages 68 and 69)
    url: https://www.crystran.com/wp-content/uploads/2025/09/magnesium-fluoride-mgf2-data-sheet.pdf
    year: 2026
    kind: datasheet
    license: supplier document, linked not reproduced
  crystran-mgf2-msds:
    title: 'Crystran: Safety Data Sheet, Magnesium Fluoride Optical Crystal (revision 2026)'
    id: Revision 2026, issued 6 July 2026; CAS 7783-40-6; EC 231-995-1
    url: https://www.crystran.com/wp-content/uploads/2025/09/magnesium-fluoride-mgf2-msds.pdf
    year: 2026
    kind: datasheet
    license: supplier document, linked not reproduced
  usgs-mcs2026-fluorspar:
    title: Mineral Commodity Summaries 2026, Fluorspar (USGS, Vanessa Londono)
    id: USGS MCS 2026, February 2026
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-fluorspar.pdf
    year: 2026
    kind: report
    license: public domain (USGS)
  nist-burnett-gupta-2000:
    title: 'Burnett and Gupta: Optical Materials and Detector Characterization for 193 nm and 157 nm Lithography (Future Fab International 8, 2000)'
    id: NIST publication page; keywords include CaF2 and 157 nm
    url: https://www.nist.gov/node/728211
    year: 2000
    kind: paper
    license: NIST publication page, linked not reproduced
  pubchem-cid-24617:
    title: PubChem compound record, Fluorite (calcium fluoride), CID 24617
    id: CID 24617; CaF2; molecular weight 78.07; EINECS 232-188-7
    url: https://pubchem.ncbi.nlm.nih.gov/compound/24617
    year: 2026
    kind: database
    license: public domain (NCBI)
  crs-if13145:
    title: 'Congressional Research Service: U.S. Geological Survey''s Critical Minerals List (IF13145)'
    id: IF13145; 2025 final list published 7 November 2025
    url: https://www.everycrsreport.com/reports/IF13145.html
    year: 2026
    kind: report
    license: CRS report, linked not reproduced
story:
  recipe:
    line: Calcium fluoride is the mineral fluorite in synthetic single-crystal form. Each formula unit combines one calcium atom with two fluorine atoms, and the crystal has the cubic fluorite structure. Crystran grows it by the vacuum Stockbarger technique in diameters up to about 250 mm. IR-grade material uses naturally mined fluorite, UV grades use chemically prepared raw material, and excimer-laser grades use selected material and crystal.
    parts:
      - name: Calcium
        symbol: Ca
        role: The metal. One calcium atom per formula unit, from the CaF2 formula (PubChem CID 24617).
      - name: Fluorine
        symbol: F
        role: The halogen. Two fluorine atoms per formula unit. Molecular weight 78.08 on the Crystran sheet and 78.07 on PubChem.
  risk_groups:
    - title: For people
      level: 1
      verdict: Harmful if inhaled; irritating to skin and eyes
      lead: The Crystran safety sheet for the 2026 revision gives H315 (causes skin irritation), H319 (causes serious eye irritation) and H332 (harmful if inhaled). It advises particular care when machining and when dust or particles form.
      points:
        - label: Dust
          line: The sheet gives an occupational limit of 2.5 mg/m3 long term, expressed as fluoride, and says to avoid making dust.
        - label: Toxicity
          line: The sheet says the material is toxic by ingestion and inhalation of dust, with a cumulative effect, and gives an oral LD50 above 4250 mg/kg in rats.
        - label: Scope
          line: Only the calcium fluoride sheet from this supplier was read in this run. Other suppliers' classifications are not checked here.
    - title: If it fails
      lead: The failure results come from supplier data sheets. No flight failure record was read.
      points:
        - label: Cleavage
          line: The data sheet says calcium fluoride cleaves on the (111) plane, so a crystal can split along a crystal plane.
        - label: Thermal shock
          line: The barium fluoride sheet says that material is highly susceptible to thermal shock. The calcium fluoride sheet gives no thermal shock figure.
    - title: Handling and storage
      gap: The sheets give no storage temperature or humidity limit. The safety sheet says to keep the material away from heat, strong acids and foodstuffs.
      points:
        - label: Protective equipment
          line: PVA gloves, a laboratory coat, safety goggles or glasses where chipping or dust may occur, and mechanical or local exhaust ventilation.
        - label: Incompatible materials
          line: Strong mineral acids. The sheet says the material reacts with them and that the decomposition product is hydrogen fluoride gas.
  why: Calcium fluoride is a cubic fluorite crystal with a refractive index of 1.39908 at 5 µm and a transmission range of 0.13 to 10 µm (Crystran). It is grown by the vacuum Stockbarger method in diameters up to about 250 mm, and Crystran uses it for spectroscopic windows, prisms, lenses and excimer-laser windows. Its Young's modulus is 75.8 GPa, its melting point is 1360 C, and it cleaves on the (111) plane.
  uses:
    - where: IR spectroscopy and Raman
      line: Crystran lists spectroscopic windows, prisms and lenses for IR work, and selected grades for Raman work because the material has no interfering fluorescence peaks.
    - where: Excimer-laser and UV optics
      line: Crystran says the highest-purity grades are used in the UV and as excimer-laser windows.
    - where: 157 nm lithography
      line: A 2000 NIST review of optical materials for 193 nm and 157 nm lithography covers calcium fluoride. The abstract does not print the numbers.
  can_do:
    - label: Range
      value: 0.13 to 10 µm
      line: Crystran's data table gives a transmission range of 0.13 to 10 µm. Its VUV trace is for specially qualified material.
    - label: Refraction
      value: '1.39908'
      line: Refractive index 1.39908 at 5 µm and reflection loss 5.4 percent at 5 µm, per the Crystran data table.
    - label: Heat
      value: 1360 °C
      line: Melting point 1360 C on the data sheet and the safety sheet. Thermal conductivity 9.71 W/(m·K) and thermal expansion 18.85 ppm/K (printed as 10^-6 per K).
    - label: Stiffness
      value: 75.8 GPa
      line: Young's modulus 75.8 GPa, shear modulus 33.77 GPa, bulk modulus 82.71 GPa and Poisson ratio 0.26, from the Crystran data table.
    - label: Dielectric
      value: '6.76'
      line: Dielectric constant 6.76 at 1 MHz, per the Crystran data table.
  compare: Crystran's sheets set calcium fluoride beside two sister fluorides. Barium fluoride transmits from 0.15 to 12 µm and reaches about 1 µm further into the IR than calcium fluoride for the same thickness, but it has a density of 4.89 g/cc, cleaves easily and is highly susceptible to thermal shock. Magnesium fluoride transmits from 0.12 to 7 µm, reaches the hydrogen Lyman-alpha line at 121 nm, has a density of 3.1766 g/cc and a melting point of 1255 C, and is slightly birefringent. The sheets give no side-by-side ground or space test and no cost comparison.
  compare_rows:
    - label: Heat conduction
      benchmark: thermal_conductivity
    - label: Thermal expansion
      benchmark: cte
    - label: Stiffness
      benchmark: elastic_modulus
  handling:
    - Avoid making dust when cutting, grinding or cleaning, and use PVA gloves and goggles where chipping may occur.
    - Keep the crystal away from strong acids, which give off hydrogen fluoride gas on reaction.
    - Place broken pieces in containers for disposal and avoid sharp edges, as the safety sheet advises.
  good_for:
    - IR spectroscopic windows, prisms and lenses, and Raman optics with no interfering fluorescence peaks (Crystran).
    - UV and excimer-laser windows, using the highest-purity grade (Crystran).
    - Lithography optics at 157 nm, where fused silica does not transmit (NIST review, 2000).
  watch_out:
    - Cleavage on (111). The crystal is brittle, and the data sheet names the cleavage plane.
    - Acids. Strong mineral acids react with calcium fluoride and give off hydrogen fluoride gas.
    - No space test. No ground radiation, outgassing or orbital result for calcium fluoride was found in the sources read.
    - Supply concentration. China produced 60 percent of the 2025 estimated world mine output and holds about a third of world reserves (110,000 of 330,000 thousand tons, USGS).
  verdict: Calcium fluoride is a cubic, broadband crystal from the vacuum ultraviolet to the infrared, and Crystran supplies it for spectroscopy, excimer optics and lithography. The sources read describe the optics well but give no space test, so its behaviour in orbit is not established by this profile.