{
  "spore": "profile",
  "id": "calcite",
  "spore_version": "0.2",
  "family": "carbonate",
  "name": "Optical calcite (Iceland spar, CaCO3)",
  "role": "birefringent polariser crystal",
  "category": "glasses-optics",
  "type": "optical-crystals",
  "summary": "Optical calcite is a transparent, naturally occurring crystal form of calcium carbonate (CaCO3). It is strongly birefringent: a 2026 paper in Ukrainian Journal of Physics gives a birefringence of approximately 0.172 at 589 nm, so its ordinary and extraordinary rays separate strongly. That property has made it a classic material for polarisers and retardation plates.\n",
  "best_for": "Polarisers and retardation plates, where a large birefringence matters more than hardness or acid resistance",
  "weakest_at": "Low hardness (Mohs hardness of 3) and dissolving in dilute acids",
  "identity": {
    "formula": "CaCO3",
    "cas": "471-34-1",
    "crystal_system": "trigonal",
    "space_group": "R-3c",
    "designations": [
      {
        "system": "Trade name",
        "code": "Iceland spar",
        "source": "wikipedia-calcite",
        "where": "Uses paragraph: 'A transparent variety called Iceland spar is used for optical purposes'"
      }
    ],
    "source": "apreotesei-2026",
    "where": "Section 1 (Introduction), paragraph on crystal structure. The CAS number is printed for calcium carbonate in the Sigma SDS (sigma-c6033-sds), not on the calcite pages."
  },
  "tags": {
    "environments": [],
    "stresses": [],
    "applications": [
      "optics-and-cameras"
    ]
  },
  "properties": [
    {
      "benchmark": "density",
      "label": "Density of optical calcite",
      "value": 2.71,
      "bound": "exact",
      "unit": "g/cm3",
      "scope": "material",
      "conditions": {
        "basis": "crystal; temperature not stated on the page"
      },
      "method": "Value stated in the 2026 paper, which cites earlier work for it",
      "status": "ground",
      "source": "apreotesei-2026",
      "where": "Section 1 (Introduction), paragraph on physicochemical properties",
      "source_detail": {
        "title": "Linear birefringence dispersion of uniaxial inorganic crystal calcite estimated based on channeled spectra",
        "id": "doi:10.15407/ujpe71.4.308 (Ukr. J. Phys. 71, No. 4, 308)",
        "url": "https://ujp.bitp.kiev.ua/index.php/ujp/article/download/2023972/3473/31120",
        "year": 2026,
        "kind": "paper",
        "license": "CC BY-NC-ND (as printed on the journal's article)"
      }
    },
    {
      "benchmark": "density",
      "label": "Relative density of calcium carbonate powder (Sigma C6033)",
      "value": 2.93,
      "bound": "exact",
      "unit": "g/cm3",
      "scope": "material",
      "conditions": {
        "form": "powder, not an optical-grade crystal",
        "temperature": "25 °C (77 °F), as printed"
      },
      "method": "Safety data sheet value, as printed",
      "status": "ground",
      "source": "sigma-c6033-sds",
      "where": "Section 9.1 (Physical and chemical properties), item m",
      "source_detail": {
        "title": "Safety data sheet, Calcium carbonate, Sigma-Aldrich product C6033",
        "id": "Sigma product C6033, CAS 471-34-1",
        "url": "https://isolab.ess.washington.edu//laboratory/safety/sds/calcium_carbonate.pdf",
        "year": 2016,
        "kind": "datasheet",
        "license": "vendor SDS, cited not reproduced"
      }
    },
    {
      "benchmark": "melting_point",
      "label": "Melting point of optical calcite",
      "value": 825,
      "bound": "exact",
      "unit": "°C",
      "scope": "material",
      "conditions": {
        "note": "printed as 'Decomposes'; the page gives no separate decomposition temperature"
      },
      "method": "Datasheet value, as printed",
      "status": "ground",
      "source": "crystran",
      "where": "Optical data table, row 'Melting point'",
      "source_detail": {
        "title": "Calcite (CaCO3) optical material data, Crystran",
        "id": "Crystran optical materials, calcite page",
        "url": "https://www.crystran.com/optical-materials/calcite-caco3/",
        "year": 2026,
        "kind": "datasheet",
        "license": "vendor page, cited not reproduced"
      }
    },
    {
      "benchmark": "melting_point",
      "label": "Melting point of calcium carbonate powder (Sigma C6033)",
      "value": 800,
      "bound": "exact",
      "unit": "°C",
      "scope": "material",
      "conditions": {
        "form": "powder, not an optical-grade crystal",
        "note": "printed as 'Decomposes on heating'"
      },
      "method": "Safety data sheet value, as printed",
      "status": "ground",
      "source": "sigma-c6033-sds",
      "where": "Section 9.1 (Physical and chemical properties), item e",
      "source_detail": {
        "title": "Safety data sheet, Calcium carbonate, Sigma-Aldrich product C6033",
        "id": "Sigma product C6033, CAS 471-34-1",
        "url": "https://isolab.ess.washington.edu//laboratory/safety/sds/calcium_carbonate.pdf",
        "year": 2016,
        "kind": "datasheet",
        "license": "vendor SDS, cited not reproduced"
      }
    },
    {
      "benchmark": "mohs_hardness",
      "label": "Mohs hardness of calcite",
      "value": 3,
      "bound": "exact",
      "unit": "Mohs",
      "scope": "material",
      "conditions": {
        "basis": "Mohs scale, as stated in the paper"
      },
      "method": "Value stated in the 2026 paper",
      "status": "ground",
      "source": "apreotesei-2026",
      "where": "Section 1 (Introduction), paragraph on physicochemical properties",
      "source_detail": {
        "title": "Linear birefringence dispersion of uniaxial inorganic crystal calcite estimated based on channeled spectra",
        "id": "doi:10.15407/ujpe71.4.308 (Ukr. J. Phys. 71, No. 4, 308)",
        "url": "https://ujp.bitp.kiev.ua/index.php/ujp/article/download/2023972/3473/31120",
        "year": 2026,
        "kind": "paper",
        "license": "CC BY-NC-ND (as printed on the journal's article)"
      }
    },
    {
      "benchmark": "transmission_range",
      "label": "Transmission range of optical calcite",
      "value": 0.3,
      "value_high": 2.3,
      "bound": "exact",
      "unit": "μm",
      "scope": "material",
      "conditions": {
        "basis": "as printed; no thickness or grade given on the page"
      },
      "method": "Datasheet value, as printed",
      "status": "ground",
      "source": "crystran",
      "where": "Optical data table, row 'Transmission range'",
      "source_detail": {
        "title": "Calcite (CaCO3) optical material data, Crystran",
        "id": "Crystran optical materials, calcite page",
        "url": "https://www.crystran.com/optical-materials/calcite-caco3/",
        "year": 2026,
        "kind": "datasheet",
        "license": "vendor page, cited not reproduced"
      }
    },
    {
      "benchmark": "refractive_index",
      "label": "Ordinary refractive index (no) at 0.51 μm",
      "value": 1.6653,
      "bound": "exact",
      "unit": "-",
      "scope": "material",
      "conditions": {
        "wavelength": "0.51 μm",
        "ray": "ordinary (no), as printed"
      },
      "method": "Refractive index table on the datasheet; the page's summary line gives 1.6654 at the same wavelength",
      "status": "ground",
      "source": "crystran",
      "where": "Refractive index table, row 0.51 μm",
      "source_detail": {
        "title": "Calcite (CaCO3) optical material data, Crystran",
        "id": "Crystran optical materials, calcite page",
        "url": "https://www.crystran.com/optical-materials/calcite-caco3/",
        "year": 2026,
        "kind": "datasheet",
        "license": "vendor page, cited not reproduced"
      }
    },
    {
      "benchmark": "refractive_index",
      "label": "Extraordinary refractive index (ne) at 0.51 μm",
      "value": 1.4896,
      "bound": "exact",
      "unit": "-",
      "scope": "material",
      "conditions": {
        "wavelength": "0.51 μm",
        "ray": "extraordinary (ne), as printed"
      },
      "method": "Refractive index table on the datasheet",
      "status": "ground",
      "source": "crystran",
      "where": "Refractive index table, row 0.51 μm",
      "source_detail": {
        "title": "Calcite (CaCO3) optical material data, Crystran",
        "id": "Crystran optical materials, calcite page",
        "url": "https://www.crystran.com/optical-materials/calcite-caco3/",
        "year": 2026,
        "kind": "datasheet",
        "license": "vendor page, cited not reproduced"
      }
    },
    {
      "benchmark": "refractive_index",
      "label": "Ordinary refractive index (no) at 400 nm",
      "value": 1.6782,
      "bound": "exact",
      "unit": "-",
      "scope": "material",
      "conditions": {
        "wavelength": "400 nm",
        "method_detail": "Abbe refractometer, as stated in the paper"
      },
      "method": "Table 1 measurement, principal refractive indices",
      "status": "ground",
      "source": "apreotesei-2026",
      "where": "Table 1 (Principal refractive indices and linear birefringence of calcite), row 400",
      "source_detail": {
        "title": "Linear birefringence dispersion of uniaxial inorganic crystal calcite estimated based on channeled spectra",
        "id": "doi:10.15407/ujpe71.4.308 (Ukr. J. Phys. 71, No. 4, 308)",
        "url": "https://ujp.bitp.kiev.ua/index.php/ujp/article/download/2023972/3473/31120",
        "year": 2026,
        "kind": "paper",
        "license": "CC BY-NC-ND (as printed on the journal's article)"
      }
    },
    {
      "benchmark": "refractive_index",
      "label": "Extraordinary refractive index (ne) at 400 nm",
      "value": 1.4936,
      "bound": "exact",
      "unit": "-",
      "scope": "material",
      "conditions": {
        "wavelength": "400 nm",
        "method_detail": "Abbe refractometer, as stated in the paper"
      },
      "method": "Table 1 measurement, principal refractive indices",
      "status": "ground",
      "source": "apreotesei-2026",
      "where": "Table 1 (Principal refractive indices and linear birefringence of calcite), row 400",
      "source_detail": {
        "title": "Linear birefringence dispersion of uniaxial inorganic crystal calcite estimated based on channeled spectra",
        "id": "doi:10.15407/ujpe71.4.308 (Ukr. J. Phys. 71, No. 4, 308)",
        "url": "https://ujp.bitp.kiev.ua/index.php/ujp/article/download/2023972/3473/31120",
        "year": 2026,
        "kind": "paper",
        "license": "CC BY-NC-ND (as printed on the journal's article)"
      }
    },
    {
      "benchmark": "refractive_index",
      "label": "Ordinary refractive index (no) at 550 nm",
      "value": 1.658,
      "bound": "exact",
      "unit": "-",
      "scope": "material",
      "conditions": {
        "wavelength": "550 nm",
        "method_detail": "Abbe refractometer, as stated in the paper"
      },
      "method": "Table 1 measurement, principal refractive indices",
      "status": "ground",
      "source": "apreotesei-2026",
      "where": "Table 1 (Principal refractive indices and linear birefringence of calcite), row 550",
      "source_detail": {
        "title": "Linear birefringence dispersion of uniaxial inorganic crystal calcite estimated based on channeled spectra",
        "id": "doi:10.15407/ujpe71.4.308 (Ukr. J. Phys. 71, No. 4, 308)",
        "url": "https://ujp.bitp.kiev.ua/index.php/ujp/article/download/2023972/3473/31120",
        "year": 2026,
        "kind": "paper",
        "license": "CC BY-NC-ND (as printed on the journal's article)"
      }
    },
    {
      "benchmark": "refractive_index",
      "label": "Extraordinary refractive index (ne) at 550 nm",
      "value": 1.4862,
      "bound": "exact",
      "unit": "-",
      "scope": "material",
      "conditions": {
        "wavelength": "550 nm",
        "method_detail": "Abbe refractometer, as stated in the paper"
      },
      "method": "Table 1 measurement, principal refractive indices",
      "status": "ground",
      "source": "apreotesei-2026",
      "where": "Table 1 (Principal refractive indices and linear birefringence of calcite), row 550",
      "source_detail": {
        "title": "Linear birefringence dispersion of uniaxial inorganic crystal calcite estimated based on channeled spectra",
        "id": "doi:10.15407/ujpe71.4.308 (Ukr. J. Phys. 71, No. 4, 308)",
        "url": "https://ujp.bitp.kiev.ua/index.php/ujp/article/download/2023972/3473/31120",
        "year": 2026,
        "kind": "paper",
        "license": "CC BY-NC-ND (as printed on the journal's article)"
      }
    },
    {
      "benchmark": "refractive_index",
      "label": "Ordinary refractive index (no) at 700 nm",
      "value": 1.6521,
      "bound": "exact",
      "unit": "-",
      "scope": "material",
      "conditions": {
        "wavelength": "700 nm",
        "method_detail": "Abbe refractometer, as stated in the paper"
      },
      "method": "Table 1 measurement, principal refractive indices",
      "status": "ground",
      "source": "apreotesei-2026",
      "where": "Table 1 (Principal refractive indices and linear birefringence of calcite), row 700",
      "source_detail": {
        "title": "Linear birefringence dispersion of uniaxial inorganic crystal calcite estimated based on channeled spectra",
        "id": "doi:10.15407/ujpe71.4.308 (Ukr. J. Phys. 71, No. 4, 308)",
        "url": "https://ujp.bitp.kiev.ua/index.php/ujp/article/download/2023972/3473/31120",
        "year": 2026,
        "kind": "paper",
        "license": "CC BY-NC-ND (as printed on the journal's article)"
      }
    },
    {
      "benchmark": "refractive_index",
      "label": "Extraordinary refractive index (ne) at 700 nm",
      "value": 1.4833,
      "bound": "exact",
      "unit": "-",
      "scope": "material",
      "conditions": {
        "wavelength": "700 nm",
        "method_detail": "Abbe refractometer, as stated in the paper"
      },
      "method": "Table 1 measurement, principal refractive indices",
      "status": "ground",
      "source": "apreotesei-2026",
      "where": "Table 1 (Principal refractive indices and linear birefringence of calcite), row 700",
      "source_detail": {
        "title": "Linear birefringence dispersion of uniaxial inorganic crystal calcite estimated based on channeled spectra",
        "id": "doi:10.15407/ujpe71.4.308 (Ukr. J. Phys. 71, No. 4, 308)",
        "url": "https://ujp.bitp.kiev.ua/index.php/ujp/article/download/2023972/3473/31120",
        "year": 2026,
        "kind": "paper",
        "license": "CC BY-NC-ND (as printed on the journal's article)"
      }
    },
    {
      "benchmark": "birefringence",
      "label": "Linear birefringence (ne minus no) at 550 nm",
      "value": 0.1718,
      "bound": "exact",
      "unit": "-",
      "scope": "material",
      "conditions": {
        "wavelength": "550 nm",
        "basis": "magnitude as printed in the Delta n column; the paper defines Delta n as ne minus no"
      },
      "method": "Computed from the Table 1 indices in the paper",
      "status": "ground",
      "source": "apreotesei-2026",
      "where": "Table 1, column Delta n, row 550",
      "source_detail": {
        "title": "Linear birefringence dispersion of uniaxial inorganic crystal calcite estimated based on channeled spectra",
        "id": "doi:10.15407/ujpe71.4.308 (Ukr. J. Phys. 71, No. 4, 308)",
        "url": "https://ujp.bitp.kiev.ua/index.php/ujp/article/download/2023972/3473/31120",
        "year": 2026,
        "kind": "paper",
        "license": "CC BY-NC-ND (as printed on the journal's article)"
      }
    },
    {
      "benchmark": "birefringence",
      "label": "Linear birefringence of calcite at 589 nm",
      "value": 0.172,
      "bound": "exact",
      "unit": "-",
      "scope": "material",
      "conditions": {
        "wavelength": "589 nm",
        "basis": "stated as approximately 0.172 at 589 nm in the Introduction"
      },
      "method": "Value stated in the paper's Introduction, citing refs. 1 and 4",
      "status": "ground",
      "source": "apreotesei-2026",
      "where": "Section 1 (Introduction), paragraph on negative uniaxial nature",
      "source_detail": {
        "title": "Linear birefringence dispersion of uniaxial inorganic crystal calcite estimated based on channeled spectra",
        "id": "doi:10.15407/ujpe71.4.308 (Ukr. J. Phys. 71, No. 4, 308)",
        "url": "https://ujp.bitp.kiev.ua/index.php/ujp/article/download/2023972/3473/31120",
        "year": 2026,
        "kind": "paper",
        "license": "CC BY-NC-ND (as printed on the journal's article)"
      }
    },
    {
      "benchmark": "thermal_conductivity",
      "label": "Thermal conductivity, para direction",
      "value": 5.526,
      "bound": "exact",
      "unit": "W m-1 K-1",
      "scope": "material",
      "conditions": {
        "direction": "para, as printed (the page does not define the axis)",
        "temperature": "273 K"
      },
      "method": "Datasheet value, as printed",
      "status": "ground",
      "source": "crystran",
      "where": "Optical data table, row 'Thermal conductivity'",
      "source_detail": {
        "title": "Calcite (CaCO3) optical material data, Crystran",
        "id": "Crystran optical materials, calcite page",
        "url": "https://www.crystran.com/optical-materials/calcite-caco3/",
        "year": 2026,
        "kind": "datasheet",
        "license": "vendor page, cited not reproduced"
      }
    },
    {
      "benchmark": "thermal_conductivity",
      "label": "Thermal conductivity, perp direction",
      "value": 4.646,
      "bound": "exact",
      "unit": "W m-1 K-1",
      "scope": "material",
      "conditions": {
        "direction": "perp, as printed (the page does not define the axis)",
        "temperature": "273 K"
      },
      "method": "Datasheet value, as printed",
      "status": "ground",
      "source": "crystran",
      "where": "Optical data table, row 'Thermal conductivity'",
      "source_detail": {
        "title": "Calcite (CaCO3) optical material data, Crystran",
        "id": "Crystran optical materials, calcite page",
        "url": "https://www.crystran.com/optical-materials/calcite-caco3/",
        "year": 2026,
        "kind": "datasheet",
        "license": "vendor page, cited not reproduced"
      }
    },
    {
      "benchmark": "specific_heat",
      "label": "Specific heat capacity of calcite",
      "value": 852,
      "bound": "exact",
      "unit": "J Kg-1 K-1",
      "scope": "material",
      "conditions": {
        "temperature": "not given on the page"
      },
      "method": "Datasheet value, as printed",
      "status": "ground",
      "source": "crystran",
      "where": "Optical data table, row 'Specific heat capacity'",
      "source_detail": {
        "title": "Calcite (CaCO3) optical material data, Crystran",
        "id": "Crystran optical materials, calcite page",
        "url": "https://www.crystran.com/optical-materials/calcite-caco3/",
        "year": 2026,
        "kind": "datasheet",
        "license": "vendor page, cited not reproduced"
      }
    },
    {
      "benchmark": "elastic_modulus",
      "label": "Young's modulus, para direction",
      "value": 88.19,
      "bound": "exact",
      "unit": "GPa",
      "scope": "material",
      "conditions": {
        "direction": "para, as printed (the page does not define the axis)"
      },
      "method": "Datasheet value, as printed",
      "status": "ground",
      "source": "crystran",
      "where": "Optical data table, row 'Young's modulus (E)'",
      "source_detail": {
        "title": "Calcite (CaCO3) optical material data, Crystran",
        "id": "Crystran optical materials, calcite page",
        "url": "https://www.crystran.com/optical-materials/calcite-caco3/",
        "year": 2026,
        "kind": "datasheet",
        "license": "vendor page, cited not reproduced"
      }
    },
    {
      "benchmark": "elastic_modulus",
      "label": "Young's modulus, perp direction",
      "value": 72.35,
      "bound": "exact",
      "unit": "GPa",
      "scope": "material",
      "conditions": {
        "direction": "perp, as printed (the page does not define the axis)"
      },
      "method": "Datasheet value, as printed",
      "status": "ground",
      "source": "crystran",
      "where": "Optical data table, row 'Young's modulus (E)'",
      "source_detail": {
        "title": "Calcite (CaCO3) optical material data, Crystran",
        "id": "Crystran optical materials, calcite page",
        "url": "https://www.crystran.com/optical-materials/calcite-caco3/",
        "year": 2026,
        "kind": "datasheet",
        "license": "vendor page, cited not reproduced"
      }
    },
    {
      "benchmark": "shear_modulus",
      "label": "Shear modulus of calcite",
      "value": 35,
      "bound": "exact",
      "unit": "GPa",
      "scope": "material",
      "conditions": {
        "basis": "single value on the page; direction not stated"
      },
      "method": "Datasheet value, as printed",
      "status": "ground",
      "source": "crystran",
      "where": "Optical data table, row 'Shear modulus (G)'",
      "source_detail": {
        "title": "Calcite (CaCO3) optical material data, Crystran",
        "id": "Crystran optical materials, calcite page",
        "url": "https://www.crystran.com/optical-materials/calcite-caco3/",
        "year": 2026,
        "kind": "datasheet",
        "license": "vendor page, cited not reproduced"
      }
    },
    {
      "benchmark": "bulk_modulus",
      "label": "Bulk modulus of calcite",
      "value": 129.53,
      "bound": "exact",
      "unit": "GPa",
      "scope": "material",
      "conditions": {
        "basis": "single value on the page; direction not stated"
      },
      "method": "Datasheet value, as printed",
      "status": "ground",
      "source": "crystran",
      "where": "Optical data table, row 'Bulk modulus (K)'",
      "source_detail": {
        "title": "Calcite (CaCO3) optical material data, Crystran",
        "id": "Crystran optical materials, calcite page",
        "url": "https://www.crystran.com/optical-materials/calcite-caco3/",
        "year": 2026,
        "kind": "datasheet",
        "license": "vendor page, cited not reproduced"
      }
    },
    {
      "benchmark": "dielectric_constant",
      "label": "Dielectric constant, para direction",
      "value": 8,
      "bound": "exact",
      "unit": "-",
      "scope": "material",
      "conditions": {
        "direction": "para, as printed",
        "frequency": "10 kHz",
        "temperature": "293 K"
      },
      "method": "Datasheet value, as printed",
      "status": "ground",
      "source": "crystran",
      "where": "Optical data table, row 'Dielectric constant'",
      "source_detail": {
        "title": "Calcite (CaCO3) optical material data, Crystran",
        "id": "Crystran optical materials, calcite page",
        "url": "https://www.crystran.com/optical-materials/calcite-caco3/",
        "year": 2026,
        "kind": "datasheet",
        "license": "vendor page, cited not reproduced"
      }
    },
    {
      "benchmark": "dielectric_constant",
      "label": "Dielectric constant, perp direction",
      "value": 8.5,
      "bound": "exact",
      "unit": "-",
      "scope": "material",
      "conditions": {
        "direction": "perp, as printed",
        "frequency": "10 kHz",
        "temperature": "293 K"
      },
      "method": "Datasheet value, as printed",
      "status": "ground",
      "source": "crystran",
      "where": "Optical data table, row 'Dielectric constant'",
      "source_detail": {
        "title": "Calcite (CaCO3) optical material data, Crystran",
        "id": "Crystran optical materials, calcite page",
        "url": "https://www.crystran.com/optical-materials/calcite-caco3/",
        "year": 2026,
        "kind": "datasheet",
        "license": "vendor page, cited not reproduced"
      }
    },
    {
      "benchmark": "water_solubility",
      "label": "Solubility of calcite in water",
      "value": 0.0014,
      "bound": "exact",
      "unit": "g/100g water",
      "scope": "material",
      "conditions": {
        "temperature": "25 °C, as printed"
      },
      "method": "Datasheet value, as printed",
      "status": "ground",
      "source": "crystran",
      "where": "Optical data table, row 'Solubility'",
      "source_detail": {
        "title": "Calcite (CaCO3) optical material data, Crystran",
        "id": "Crystran optical materials, calcite page",
        "url": "https://www.crystran.com/optical-materials/calcite-caco3/",
        "year": 2026,
        "kind": "datasheet",
        "license": "vendor page, cited not reproduced"
      }
    },
    {
      "benchmark": "elastic_limit",
      "label": "Apparent elastic limit of calcite",
      "value": 4.83,
      "bound": "exact",
      "unit": "MPa",
      "scope": "material",
      "conditions": {
        "basis": "apparent elastic limit as printed; the test method is not described"
      },
      "method": "Datasheet value, as printed",
      "status": "ground",
      "source": "crystran",
      "where": "Optical data table, row 'Apparent elastic limit'",
      "source_detail": {
        "title": "Calcite (CaCO3) optical material data, Crystran",
        "id": "Crystran optical materials, calcite page",
        "url": "https://www.crystran.com/optical-materials/calcite-caco3/",
        "year": 2026,
        "kind": "datasheet",
        "license": "vendor page, cited not reproduced"
      }
    }
  ],
  "corrosion": [
    {
      "environment": "Dilute acids",
      "headline": "Calcite dissolves in dilute acids.",
      "effect": "Wikipedia states that calcite is soluble in dilute acids. The 2026 paper says its susceptibility to acidic environments requires protective measures during handling.",
      "rating": "severe",
      "conditions": {
        "concentration": "dilute acid; strength not stated in the sources"
      },
      "source": "wikipedia-calcite",
      "where": "Properties section, solubility statement"
    },
    {
      "environment": "Water at 25 °C",
      "headline": "Very low solubility in water.",
      "effect": "Crystran lists a solubility of 0.0014g/100g water at 25°C. The 2026 paper describes calcite's solubility in water as low.",
      "rating": "low",
      "conditions": {
        "temperature": "25 °C"
      },
      "source": "crystran",
      "where": "Optical data table, row 'Solubility'"
    }
  ],
  "risks": {
    "hazards": [
      {
        "text": "PubChem's GHS summary for calcium carbonate (CID 10112) lists the ECHA entries as 'Not Classified'. Most company reports say the substance does not meet GHS hazard criteria.",
        "ghs": [],
        "source": "pubchem-ghs",
        "where": "GHS Classification, ECHA entries"
      },
      {
        "text": "The Sigma safety data sheet for calcium carbonate powder (product C6033) says: 'Not a hazardous substance or mixture.' Its toxicology section records mild eye irritation in rabbits (OECD Test Guideline 405).",
        "ghs": [],
        "source": "sigma-c6033-sds",
        "where": "Section 2.1 and 2.2; Section 11.1, eye irritation"
      }
    ],
    "failure_risks": [
      {
        "mode": "Cleavage fracture",
        "trigger": "Mechanical stress along the crystal's cleavage planes",
        "consequence": "Calcite has perfect cleavage along rhombohedral planes, so a crystal can split along them.",
        "severity": "moderate",
        "source": "wikipedia-calcite",
        "where": "Cleavage paragraph"
      },
      {
        "mode": "Acid attack",
        "trigger": "Contact with dilute acid",
        "consequence": "The crystal dissolves, and the 2026 paper says protective measures are needed during handling.",
        "severity": "high",
        "source": "wikipedia-calcite",
        "where": "Properties section, solubility statement"
      },
      {
        "mode": "Heating past its decomposition point",
        "trigger": "Heating to its melting or decomposition point",
        "consequence": "Crystran prints the melting point as 825 °C with 'Decomposes'. Wikipedia describes calcite as infusible and says it decrepitates energetically.",
        "severity": "low",
        "source": "crystran",
        "where": "Optical data table, row 'Melting point'"
      }
    ],
    "side_effects": [],
    "handling": [
      {
        "text": "Keep the powder container tightly closed in a dry and well-ventilated place. The Sigma SDS says the powder is moisture sensitive.",
        "source": "sigma-c6033-sds"
      },
      {
        "text": "Avoid dust formation and use exhaust ventilation where dust forms, according to the Sigma SDS.",
        "source": "sigma-c6033-sds"
      },
      {
        "text": "Keep the material away from strong oxidizing agents, acids, magnesium and aluminium, according to the Sigma SDS.",
        "source": "sigma-c6033-sds"
      }
    ],
    "mitigations": [
      {
        "text": "Where nuisance dust is a concern, the Sigma SDS advises an N95 (US) or P1 (EN 143) dust mask.",
        "source": "sigma-c6033-sds"
      }
    ]
  },
  "uses": [
    {
      "application": "optics-and-cameras",
      "device": "Polarisers and retardation plates",
      "example": "Crystran describes calcite as a strongly birefringent material used for polarisers and retardation plates.",
      "source": "crystran",
      "where": "Description paragraph"
    },
    {
      "application": "optics-and-cameras",
      "device": "Optical path compensators, multi-order wave-plates and Wood-type polarisers",
      "example": "The 2026 paper lists these uses, which exploit the contrast between the ordinary and extraordinary indices.",
      "source": "apreotesei-2026",
      "where": "Section 1 (Introduction)"
    },
    {
      "application": "optics-and-cameras",
      "device": "Gun sights and bomb sights in World War II",
      "example": "Wikipedia states that high-grade optical calcite was used in gun sights, including bomb sights and anti-aircraft weapons, during World War II.",
      "source": "wikipedia-calcite",
      "where": "History of use section"
    }
  ],
  "supply": [
    {
      "subject": "Calcium carbonate feedstock (crushed stone, limestone)",
      "abundance": "USGS: stone resources are plentiful throughout the world, but the supply of high-purity limestone and dolomite suitable for specialty uses is limited in many geographic areas.",
      "producers": [],
      "critical_lists": [],
      "recycling": "Not stated for calcite in the sources we hold.",
      "substitutes": [],
      "source": "usgs-mcs2026-stone",
      "where": "World Resources paragraph"
    },
    {
      "subject": "Optical-grade calcite (Iceland spar)",
      "abundance": "Wikipedia says the Helgustadir mine in Iceland was once the main source of Iceland spar. The site is now a nature reserve, and calcite mining is no longer allowed there.",
      "producers": [],
      "critical_lists": [],
      "recycling": "Not stated for calcite in the sources we hold.",
      "substitutes": [],
      "source": "wikipedia-calcite",
      "where": "Iceland spar paragraph"
    }
  ],
  "media": [],
  "documents": [
    {
      "title": "Sigma-Aldrich safety data sheet, Calcium carbonate, product C6033, version 5.8, revision 05/24/2016",
      "type": "sds",
      "url": "https://isolab.ess.washington.edu//laboratory/safety/sds/calcium_carbonate.pdf",
      "year": 2016
    },
    {
      "title": "PubChem: calcium carbonate (CID 10112), GHS classification",
      "type": "database",
      "url": "https://pubchem.ncbi.nlm.nih.gov/rest/pug_view/data/compound/10112/JSON?heading=GHS+Classification",
      "year": 2026
    },
    {
      "title": "Linear birefringence dispersion of uniaxial inorganic crystal calcite estimated based on channeled spectra (Ukr. J. Phys. 71, No. 4, 308)",
      "type": "paper",
      "url": "https://ujp.bitp.kiev.ua/index.php/ujp/article/download/2023972/3473/31120",
      "year": 2026
    },
    {
      "title": "USGS Mineral Commodity Summaries 2026: Stone (Crushed)",
      "type": "report",
      "url": "https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-stone-crushed.pdf",
      "year": 2026
    }
  ],
  "gaps": [
    "Thermal expansion and the temperature coefficient of refractive index are printed in exponent notation on the Crystran page, so they were left out.",
    "Knoop hardness is printed without a unit on the Crystran page, so it was left out.",
    "Growth method and manufacturing process for optical-grade calcite were not stated in the sources we hold.",
    "No producer country shares for optical-grade calcite were found; the USGS stone summary gives none for this commodity.",
    "No critical-minerals list status for calcium carbonate was found in the sources we hold.",
    "No flight, vacuum or radiation test data for calcite were found. The planetary use mentioned in the 2026 paper is not tested in space in any source we hold.",
    "Hazard data come from a calcium carbonate powder SDS and PubChem, not from an SDS for an optical-grade calcite crystal.",
    "Heat and humidity ageing of the crystal were not found in the sources we hold.",
    "Dispersion coefficients (Ghosh 1999, shown on refractiveindex.info) are printed as a formula with exponents, so no values were recorded from them.",
    "The CAS number is printed for calcium carbonate in the Sigma SDS, not for optical calcite on the calcite pages."
  ],
  "story": {
    "why": "Optical calcite is a transparent crystal form of calcium carbonate with a trigonal structure. It is used where its strong birefringence is needed, so that ordinary and extraordinary light can be separated and controlled. The same crystal is soft and dissolves in acid, so it suits instruments and polarising optics more than structural or chemically exposed parts.",
    "uses": [
      {
        "where": "Polarisers and retardation plates",
        "line": "Crystran describes calcite as a strongly birefringent material used for polarisers and retardation plates. The 2026 paper lists optical path compensators, multi-order wave-plates and Wood-type polarisers as uses."
      },
      {
        "where": "Historical polarisers and wartime sights",
        "line": "Wikipedia says calcite was used as a polarizer in Nicol prisms before Polaroid plates were invented. During World War II, high-grade optical calcite was used in gun sights, including bomb sights and anti-aircraft weapons."
      }
    ],
    "can_do": [
      {
        "label": "Polarisation",
        "line": "Separates light into ordinary and extraordinary rays, which is the basis of polarisers and retardation plates (Crystran; Apreotesei et al. 2026).",
        "scope": "material"
      },
      {
        "label": "Birefringence",
        "line": "The 2026 paper states this value, which is large enough for compact polarising optics.",
        "benchmark": "birefringence",
        "scope": "material",
        "value": "approximately 0.172 at 589 nm"
      },
      {
        "label": "Transmission",
        "line": "The transmission range printed by Crystran.",
        "scope": "material",
        "value": "0.3 to 2.3 μm"
      },
      {
        "label": "Reference standard",
        "line": "The 2026 paper says calcite is used as a reference standard for characterising uniaxial media.",
        "scope": "material"
      }
    ],
    "compare": "The density of optical calcite is recorded as 2.71 g/cm3 in the 2026 paper, and Crystran's table gives the same value. The Sigma safety data sheet prints a relative density of 2.93 g/cm3 at 25 °C for calcium carbonate powder. The two values describe different product forms, so the gap between them is not a grade comparison. Optical calcite's melting point of 825 °C (Crystran, decomposes) is also above the 800 °C (decomposes) printed for the powder, but both are reported only as decomposition points.",
    "compare_rows": [
      {
        "label": "Birefringence at 589 nm",
        "benchmark": "birefringence",
        "scope": "material"
      },
      {
        "label": "Melting point (decomposes)",
        "benchmark": "melting_point",
        "scope": "material"
      },
      {
        "label": "Mohs hardness",
        "benchmark": "mohs_hardness",
        "scope": "material"
      }
    ],
    "handling": [
      "Keep the material dry and sealed, away from acids and strong oxidizers (Sigma SDS for the powder).",
      "Avoid dust, and use exhaust ventilation where dust forms (Sigma SDS).",
      "Protect optical calcite from acidic environments during handling, as the 2026 paper advises."
    ],
    "good_for": [
      "Polarisers and retardation plates, where a large birefringence is the main requirement (Crystran; Apreotesei et al. 2026).",
      "Historical and instrument optics, where its polarising role is established (Wikipedia)."
    ],
    "watch_out": [
      "Low hardness of Mohs hardness of 3, so it scratches easily and needs careful polishing.",
      "Dissolves in dilute acids, so it does not suit acid environments.",
      "Cleaves along rhombohedral planes under mechanical stress."
    ],
    "verdict": "Calcite is the classic choice for polarising optics where birefringence matters most. It is a poor choice for acid environments or for parts that need hardness.",
    "recipe": {
      "line": "Calcite is calcium carbonate, CaCO3. Each formula unit combines one calcium ion with one carbonate group, which is one carbon atom bonded to three oxygen atoms in a planar arrangement. Natural crystals differ in their refractive indices depending on how they grew (Apreotesei et al. 2026).",
      "parts": [
        {
          "name": "Calcium",
          "symbol": "Ca",
          "role": "Ca2+ ions sit between the planar carbonate groups and add to the crystal's mechanical stability."
        },
        {
          "name": "Carbon",
          "symbol": "C",
          "role": "The central atom of each carbonate group."
        },
        {
          "name": "Oxygen",
          "symbol": "O",
          "role": "Three oxygen atoms per carbonate group, bonded to the carbon in a planar, trigonal arrangement."
        }
      ]
    },
    "risk_groups": [
      {
        "title": "For people",
        "lead": "The calcium carbonate powder SDS we checked does not classify the material as hazardous. Its toxicology section records mild eye irritation.",
        "points": [
          {
            "label": "The powder",
            "line": "The Sigma SDS for product C6033 says 'Not a hazardous substance or mixture'. PubChem's ECHA-based entries also list the substance as Not Classified."
          },
          {
            "label": "Dust",
            "line": "The SDS advises avoiding dust and using an N95 (US) or P1 (EN 143) mask where nuisance dust is a concern."
          },
          {
            "label": "Eyes",
            "line": "The SDS reports mild eye irritation in rabbits under OECD Test Guideline 405."
          }
        ],
        "verdict": "Not classified hazardous in the SDS we checked"
      },
      {
        "title": "For the crystal",
        "lead": "Calcite's own properties limit where it can be used, more than any hazard to people.",
        "points": [
          {
            "label": "Acids",
            "line": "Calcite dissolves in dilute acids, and the 2026 paper says protective measures are needed during handling."
          },
          {
            "label": "Cleavage",
            "line": "Calcite has perfect cleavage along rhombohedral planes, so it can split along them under stress."
          },
          {
            "label": "Heat",
            "line": "Crystran prints the melting point as 825 °C with 'Decomposes'. Wikipedia describes calcite as infusible and says it decrepitates energetically."
          }
        ],
        "verdict": "Dissolves in dilute acid and cleaves easily"
      }
    ]
  },
  "updated": "2026-11-02",
  "review": {
    "status": "draft",
    "method": "assistant",
    "checked_values": 27,
    "unreachable": 0,
    "caveats": 0,
    "note": "Drafted on 2026-11-02 by an AI assistant from pages read in this run."
  },
  "sources": {
    "crystran": {
      "title": "Calcite (CaCO3) optical material data, Crystran",
      "id": "Crystran optical materials, calcite page",
      "url": "https://www.crystran.com/optical-materials/calcite-caco3/",
      "year": 2026,
      "kind": "datasheet",
      "license": "vendor page, cited not reproduced"
    },
    "wikipedia-calcite": {
      "title": "Calcite, Wikipedia",
      "id": "Wikipedia article: Calcite",
      "url": "https://en.wikipedia.org/wiki/Calcite",
      "year": 2026,
      "kind": "web",
      "license": "CC BY-SA 4.0"
    },
    "apreotesei-2026": {
      "title": "Linear birefringence dispersion of uniaxial inorganic crystal calcite estimated based on channeled spectra",
      "id": "doi:10.15407/ujpe71.4.308 (Ukr. J. Phys. 71, No. 4, 308)",
      "url": "https://ujp.bitp.kiev.ua/index.php/ujp/article/download/2023972/3473/31120",
      "year": 2026,
      "kind": "paper",
      "license": "CC BY-NC-ND (as printed on the journal's article)"
    },
    "pubchem-cid10112": {
      "title": "PubChem compound summary: calcium carbonate (CID 10112)",
      "id": "CID 10112",
      "url": "https://pubchem.ncbi.nlm.nih.gov/rest/pug/compound/name/calcite/property/MolecularFormula,MolecularWeight,InChIKey/JSON",
      "year": 2026,
      "kind": "database",
      "license": "public domain (NIH PubChem)"
    },
    "pubchem-ghs": {
      "title": "PubChem GHS classification for CID 10112 (ECHA aggregated reports)",
      "id": "CID 10112, GHS Classification",
      "url": "https://pubchem.ncbi.nlm.nih.gov/rest/pug_view/data/compound/10112/JSON?heading=GHS+Classification",
      "year": 2026,
      "kind": "database",
      "license": "public domain (NIH PubChem)"
    },
    "sigma-c6033-sds": {
      "title": "Safety data sheet, Calcium carbonate, Sigma-Aldrich product C6033",
      "id": "Sigma product C6033, CAS 471-34-1",
      "url": "https://isolab.ess.washington.edu//laboratory/safety/sds/calcium_carbonate.pdf",
      "year": 2016,
      "kind": "datasheet",
      "license": "vendor SDS, cited not reproduced"
    },
    "usgs-mcs2026-stone": {
      "title": "Mineral Commodity Summaries 2026: Stone (Crushed)",
      "id": "USGS Mineral Commodity Summaries, February 2026",
      "url": "https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-stone-crushed.pdf",
      "year": 2026,
      "kind": "report",
      "license": "public domain (USGS)"
    },
    "refractiveindex-ghosh": {
      "title": "refractiveindex.info entry for calcite, ordinary index (Ghosh 1999 dispersion)",
      "id": "Polyanskiy M. N., Sci. Data 11, 94 (2024); Ghosh G., Opt. Commun. 163, 95-102 (1999)",
      "url": "https://refractiveindex.info/?shelf=main&book=CaCO3&page=Ghosh-o",
      "year": 2024,
      "kind": "database",
      "license": "site terms not checked"
    }
  },
  "license": "CC-BY-4.0",
  "url": "https://spacemushroom.com/profiles/calcite/"
}