spore: profile
id: erbium
spore_version: 0.2
family: rare-earth-metals
name: Erbium
abbreviation: Er
role: optical fibre amplifier dopant and near-infrared laser ion
category: metals
type: heavy-metals
summary: |
  Erbium is the element Er (atomic number 68), a soft, silvery lanthanide metal with a density of 9.065 g/cm3 at 20 °C and a melting point of 1529 °C (Wikipedia). Its principal commercial sources are the minerals xenotime and euxenite, and it is also found in monazite and bastnasite (Wikipedia). Its best known use is as the active element in erbium-doped optical silica fibre, used in fibre amplifiers for long-distance optical links (Wikipedia). A compact erbium-doped amplifier with an output above 2 W has been designed for a 6U CubeSat in low Earth orbit (NICT). In fine form the metal is classed as a flammable solid (PubChem H228), and it reacts with hot water and dilute acids. The USGS reports that China supplied 71 % of U.S. imports of rare-earth compounds and metals in 2021 to 2024, and that China added erbium to its export controls in October.
best_for: Optical fibre amplifiers, where erbium is the active dopant in silica fibre (Wikipedia)
weakest_at: Fine metal is flammable (PubChem H228), and the metal reacts with hot water and dilute acids and tarnishes in moist air (Wikipedia, Stanford Advanced Materials)
identity:
  formula: Er (element, atomic number 68); hexagonal close-packed crystal structure at room temperature (Wikipedia)
  cas: 7440-52-0
  source: pubchem-er
  where: Other Identifiers, CAS entry (PubChem CID 23980)
tags:
  environments:
    - low-earth-orbit
  applications:
    - optics-and-cameras
properties:
  - benchmark: density
    label: Density, erbium at 20 °C
    value: 9.065
    unit: g/cm3
    scope: material
    conditions:
      temperature: 20 °C
      unit_in_source: 9.065 g/cm3
    method: Value printed in the Wikipedia infobox, Density (at 20° C) row
    status: ground
    source: wikipedia-er
    where: Infobox, row Density (at 20° C)
  - benchmark: density
    label: Density, erbium foil at 20 °C
    value: 9.051
    unit: g/cm3
    scope: material
    conditions:
      temperature: 20 °C
      form: foil, 99 % (2N) light tight
    method: Value printed in a supplier product datasheet
    status: ground
    note: The Wikipedia infobox gives 9.065 g/cm3 for the bulk metal, so the two values differ by 0.014 g/cm3.
    source: goodfellow-er-foil
    where: Physical properties table, row Density (9.051@20°C)
  - benchmark: density
    label: Specific gravity, erbium metal
    value: 9.01
    unit: g/cm3
    scope: material
    conditions:
      unit_in_source: 9.01 G/CC
      basis: specific gravity, water = 1
    method: Value printed in a safety data sheet, Section III Physical/Chemical Characteristics
    status: ground
    source: sam-er-msds
    where: Section III, row Specific gravity (water=1)
  - benchmark: melting_point
    label: Melting point, erbium
    value: 1529
    unit: °C
    scope: material
    conditions:
      unit_in_source: 1802 K (1529 °C, 2784 °F)
      pressure: not stated
    method: Value printed in the Wikipedia infobox, Melting point row
    status: ground
    source: wikipedia-er
    where: Infobox, row Melting point
  - benchmark: melting_point
    label: Melting point, erbium metal (safety data sheet)
    value: 1529
    unit: °C
    scope: material
    conditions:
      unit_in_source: 1529.0°C
    method: Value printed in a safety data sheet, Section III Freezing/Melting Point
    status: ground
    source: sam-er-msds
    where: Section III, Freezing/Melting Point
  - benchmark: melting_point
    label: Melting point, erbium foil
    value: 1529
    unit: °C
    scope: material
    conditions:
      form: foil, 99 % (2N) light tight
    method: Value printed in a supplier product datasheet
    status: ground
    source: goodfellow-er-foil
    where: Thermal properties table, row Melting point (C) 1529
  - benchmark: boiling_point
    label: Boiling point, erbium
    value: 2868
    unit: °C
    scope: material
    conditions:
      unit_in_source: 3141 K (2868 °C, 5194 °F)
      pressure: not stated in the infobox
    method: Value printed in the Wikipedia infobox, Boiling point row
    status: ground
    note: The safety data sheet and the foil datasheet give 2863 °C, so the sources differ by 5 °C. Both are recorded.
    source: wikipedia-er
    where: Infobox, row Boiling point
  - benchmark: boiling_point
    label: Boiling point, erbium metal (safety data sheet)
    value: 2863
    unit: °C
    scope: material
    conditions:
      unit_in_source: 2863.0°C
    method: Value printed in a safety data sheet, Section III Boiling Point
    status: ground
    source: sam-er-msds
    where: Section III, Boiling Point
  - benchmark: boiling_point
    label: Boiling point, erbium foil
    value: 2863
    unit: °C
    scope: material
    conditions:
      form: foil, 99 % (2N) light tight
    method: Value printed in a supplier product datasheet
    status: ground
    source: goodfellow-er-foil
    where: Physical properties table, row Boiling point (C) 2863
  - benchmark: thermal_conductivity
    label: Thermal conductivity, erbium
    value: 14.5
    unit: W/(m⋅K)
    scope: material
    conditions:
      temperature: not stated
      unit_in_source: 14.5 W/(m⋅K)
    method: Value printed in the Wikipedia infobox; no temperature is given
    status: ground
    source: wikipedia-er
    where: Infobox, row Thermal conductivity
  - benchmark: electrical_resistivity
    label: Electrical resistivity, polycrystalline erbium at room temperature
    value: 0.86
    unit: µΩ⋅m
    scope: material
    conditions:
      temperature: r.t. (room temperature, as printed)
      form: polycrystalline (poly)
      unit_in_source: 0.860 µΩ⋅m
    method: Value printed in the Wikipedia infobox, Electrical resistivity row
    status: ground
    source: wikipedia-er
    where: Infobox, row Electrical resistivity, poly
  - benchmark: elastic_modulus
    label: Young's modulus, erbium
    value: 69.9
    unit: GPa
    scope: material
    conditions:
      temperature: not stated
    method: Value printed in the Wikipedia infobox
    status: ground
    source: wikipedia-er
    where: Infobox, row Young's modulus
  - benchmark: vickers_hardness
    label: Vickers hardness, erbium
    value: 430
    value_high: 700
    unit: MPa
    scope: material
    conditions:
      temperature: not stated
      unit_in_source: 430–700 MPa
    method: Range printed in the Wikipedia infobox, Vickers hardness row
    status: ground
    note: No canonical name exists for hardness in the property file, so vickers_hardness is a new name and is listed in gaps.
    source: wikipedia-er
    where: Infobox, row Vickers hardness
  - benchmark: brinell_hardness
    label: Brinell hardness, erbium
    value: 600
    value_high: 1070
    unit: MPa
    scope: material
    conditions:
      temperature: not stated
      unit_in_source: 600–1070 MPa
    method: Range printed in the Wikipedia infobox, Brinell hardness row
    status: ground
    note: No canonical name exists for Brinell hardness in the property file, so brinell_hardness is a new name and is listed in gaps.
    source: wikipedia-er
    where: Infobox, row Brinell hardness
corrosion:
  - environment: Moist air
    headline: Erbium keeps its lustre in dry air but tarnishes slowly in moist air.
    effect: Wikipedia says erbium retains its luster in dry air but will slowly tarnish in moist air, and that it burns readily to form erbium(III) oxide. No temperature is given.
    rating: moderate
    conditions:
      atmosphere: dry air and moist air
      temperature: not stated
    source: wikipedia-er
    where: Chemical properties, Air paragraph
  - environment: Cold and hot water
    headline: Erbium reacts slowly with cold water and quite quickly with hot water.
    effect: Wikipedia gives the reaction rates without temperatures. The safety data sheet lists water and moisture among the materials erbium is incompatible with.
    rating: severe
    conditions:
      temperature: not stated
    source: wikipedia-er
    where: Chemical properties, Water paragraph
  - environment: Dilute acids
    headline: Erbium dissolves readily in dilute sulfuric acid and releases flammable hydrogen gas.
    effect: Wikipedia says erbium dissolves readily in dilute sulfuric acid. The safety data sheet says the metal reacts with dilute acids and emits flammable and explosive hydrogen gas.
    rating: severe
    conditions:
      acid: dilute sulfuric acid, and dilute acids in general
      temperature: not stated
    source: sam-er-msds
    where: Section IV Fire and Explosion Hazard Data; Section VI Reactivity Data
  - environment: Air, moisture, acids, oxidizing materials and halogens
    headline: The safety data sheet lists air, moisture, acids, oxidizers and halogens as incompatible materials.
    effect: The sheet lists these as incompatibilities and gives hydrogen as the decomposition product. No rate or threshold is given.
    rating: moderate
    conditions:
      form: metal
    source: sam-er-msds
    where: Section VI Reactivity Data, Incompatibility
risks:
  hazards:
    - text: 'PubChem GHS summary, ECHA C&L notifications: H228 (93.3 %): Flammable solid, signal word Danger, class Flam. Sol. 1. Of 104 company reports, 5 (4.8 %) say the substance does not meet GHS criteria, so classification depends on the notifier and the form.'
      ghs:
        - H228
      source: pubchem-er
      where: Safety and Hazards, Hazards Identification, GHS Classification
    - text: Goodfellow erbium foil product page shows a GHS02 Flammable pictogram and a shipping restriction note.
      ghs: []
      source: goodfellow-er-foil
      where: Hazards section of the product page
    - text: 'Safety data sheet, erbium metal (Stanford Advanced Materials, revised 2012): the sheet gives no GHS hazard statements. It says the chemical, physical and toxicological properties have not been thoroughly investigated. Fumes from a fire are hazardous.'
      ghs: []
      source: sam-er-msds
      where: Section V Health Hazard Data, opening paragraph; Section IV Special Fire Fighting Procedures
  failure_risks:
    - mode: Fire in fine metal
      trigger: Finely divided erbium exposed to a flame or spark
      consequence: PubChem quotes Hawley that fine metal is flammable. The Goodfellow sheet carries the flammable pictogram.
      severity: moderate
      source: pubchem-er
      where: Safety and Hazards, Hazards Summary
    - mode: Hydrogen release on contact with acid
      trigger: Erbium metal in contact with dilute acids
      consequence: The metal emits flammable and explosive hydrogen gas (Stanford Advanced Materials).
      severity: critical
      source: sam-er-msds
      where: Section IV Special Fire Fighting Procedures
    - mode: Reaction with hot water
      trigger: Erbium metal in contact with hot water
      consequence: Wikipedia says the metal reacts quite quickly with hot water, and that it reacts slowly with cold water.
      severity: moderate
      source: wikipedia-er
      where: Chemical properties, Water paragraph
    - mode: Tarnish in moist air
      trigger: Long exposure to moist air
      consequence: The surface tarnishes slowly, and the sheet gives no rate.
      severity: low
      source: wikipedia-er
      where: Chemical properties, Air paragraph
  side_effects:
    - text: Dust may cause asthma attacks and lung damage, including lung granulomas, and the skin and lungs can develop granulomas after exposure to rare earth metals (Stanford Advanced Materials).
      affects: People handling dust and fine swarf
      source: sam-er-msds
      where: Section V Health Hazard Data, Inhalation and Skin paragraphs
  handling:
    - text: Store in a cool, dry area in a tightly sealed container (Stanford Advanced Materials).
      source: sam-er-msds
      where: Section VII Hazard Label Information
    - text: Handle in a dry, controlled atmosphere. Wear a NIOSH approved respirator, impervious rubber gloves and safety glasses (Stanford Advanced Materials).
      source: sam-er-msds
      where: Section VIII Control Measures, Protective Equipment Summary and Special
    - text: Use Class D or another suitable metal extinguishing agent on fires, and do not use water (Stanford Advanced Materials).
      source: sam-er-msds
      where: Section IV Fire Extinguishing Media
    - text: Vacuum up spills with a HEPA filter and place the waste in a closed container, taking care not to raise dust (Stanford Advanced Materials).
      source: sam-er-msds
      where: Section VII Steps to be taken in case material is released or spilled
  mitigations: []
uses:
  - application: optics-and-cameras
    device: Erbium-doped optical fibre amplifiers in telecom and long-distance optical links
    example: Wikipedia says erbium-doped optical silica-glass fibres are the active element in erbium-doped fibre amplifiers.
    source: wikipedia-er
    where: Applications, Lasers and optics
  - application: optics-and-cameras
    device: Compact erbium-doped fibre amplifier for a 6U CubeSat optical terminal in low Earth orbit
    example: NICT reports a two-stage erbium-doped fibre amplifier for the CubeSOTA 6U CubeSat, with a high-power amplifier that delivers an output above 2 W. The paper gives a total ionising dose test above 20 krad and vibration and thermal vacuum tests.
    source: nict-edfa-frontiers
    where: Abstract; Section 2 Table 1; Section 3 Environmental validation
  - application: optics-and-cameras
    device: Space-qualified erbium/ytterbium fibre amplifier for satellite links
    example: Agiltron describes a vacuum-rated erbium/ytterbium amplifier for satellite communication, typically designed to function reliably for over 10 years. The page does not name a satellite or mission.
    source: agiltron-space-edfa
    where: Description and Features section
  - application: optics-and-cameras
    device: Medical erbium lasers
    example: Wikipedia says medical laser uses of erbium utilise the erbium ion's 2940 nm emission, as in Er:YAG lasers.
    source: wikipedia-er
    where: Applications, Lasers and optics
supply:
  - subject: Erbium abundance in the Earth's crust
    abundance: About 2.8 mg/kg in the Earth's crust (Wikipedia)
    producers: []
    critical_lists: []
    source: wikipedia-er
    where: Occurrence section
  - subject: Erbium ores
    abundance: The principal commercial sources are the minerals xenotime and euxenite, and erbium is also found in monazite and bastnasite (Wikipedia). Erbia is about 4 to 5 % in high-yttrium concentrates (Wikipedia).
    producers: []
    critical_lists: []
    source: wikipedia-er
    where: Occurrence and Production sections; Isotopes and natural occurrence
  - subject: Rare-earth compounds and metals, U.S. import sources 2021 to 2024 (group total, erbium not separated)
    producers:
      - country: China
        share_percent: 71
      - country: Malaysia
        share_percent: 13
      - country: Japan
        share_percent: 5
      - country: Estonia
        share_percent: 5
      - country: other
        share_percent: 6
    critical_lists: []
    source: usgs-rare-earths
    where: Import Sources (2021 to 2024) paragraph. These are U.S. import shares, not world production shares.
  - subject: World rare-earth mine production and reserves (group total, erbium not separated)
    abundance: Mine production, China 270,000 (2024) and 270,000 (2025); United States 45,500 (2024) and 51,000 (2025); world total 380,000 (2024) and 390,000 (2025). China reserves 44,000,000. Units as printed in the USGS table.
    producers: []
    critical_lists: []
    source: usgs-rare-earths
    where: Mine production and reserves table, World total row.
  - subject: Recycling and substitutes (rare earths)
    recycling: 'USGS: limited quantities of rare earths were recovered from batteries, permanent magnets and fluorescent lamps.'
    substitutes:
      - 'USGS: substitutes are available for many applications but generally are less effective.'
    critical_lists: []
    source: usgs-rare-earths
    where: Recycling paragraph; Substitutes paragraph
  - subject: Export controls on erbium
    abundance: China tightened its rare-earth export controls in April 2025, and in October it expanded them to include erbium. In November it suspended the October controls for one year.
    producers: []
    critical_lists: []
    source: usgs-rare-earths
    where: Events, Trends, and Issues
documents:
  - title: 'USGS Mineral Commodity Summaries 2026: Rare Earths'
    type: report
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-rare-earths.pdf
    year: 2026
  - title: 'Wikipedia: Erbium'
    type: database
    url: https://en.wikipedia.org/wiki/Erbium
    year: 2026
  - title: PubChem compound record for erbium (CID 23980), including ECHA C&L Inventory classification
    type: database
    url: https://pubchem.ncbi.nlm.nih.gov/compound/23980
  - title: 'Material Safety Data Sheet: Erbium Metal (Stanford Advanced Materials, revision 2.0, 2012), copy hosted by Sputtertargets.net'
    type: sds
    url: https://www.sputtertargets.net/Public/pdf/erbium-msds.pdf
    year: 2012
  - title: Erbium foil light tight group (Goodfellow product datasheet, UK)
    type: datasheet
    url: https://www.goodfellow.com/uk/erbium-foil-light-tight-group
  - title: 'Frontiers in Physics 2025: compact erbium-doped fibre amplifier for the CubeSOTA CubeSat optical terminal (NICT)'
    type: paper
    url: https://www.frontiersin.org/journals/physics/articles/10.3389/fphy.2025.1542043/full
    year: 2025
  - title: Agiltron space-qualified erbium/ytterbium small signal fibre amplifier (product page)
    type: datasheet
    url: https://agiltron.com/?p=22667
gaps:
  - Erbium is not separated in the USGS rare-earths report. The supply shares and production figures are for the rare-earth group, so no erbium-specific production share is given.
  - 'Critical-mineral listing: the USGS rare-earths text read here does not state a critical-minerals listing for erbium, so critical_lists is empty.'
  - 'World erbium production and reserves: not found in the sources read.'
  - 'PubChem record CID 23980: the JSON read gives no experimental melting point, boiling point or density, and no OSHA or NIOSH exposure limit for erbium. The safety data sheet gives PEL and TLV as NE (not established), so no exposure limit is entered.'
  - 'Designations: no UNS, EN, ASTM or trade code for erbium metal was printed by a source read in this run, so designations are left out.'
  - Vickers and Brinell hardness are entered under new names (vickers_hardness and brinell_hardness) because the property file has no canonical name for hardness. Both are printed in MPa as ranges.
  - 'Boiling point and density differ between sources: Wikipedia gives 2868 °C and 9.065 g/cm3, while the safety data sheet and the foil datasheet give 2863 °C and 9.051 to 9.01 g/cm3. All values are recorded with their sources.'
  - Melting point 1497 °C appears in American Elements and a university periodic table, but neither page could be read in full (American Elements returned HTTP 403) and the periodic table gives no unit, so it is not entered.
  - Specific heat, thermal expansion, shear modulus, Poisson's ratio, emissivity and thermal neutron cross-section for erbium were not found in the sources read.
  - Mechanical properties of erbium metal (yield, tensile, elongation) were not found in the sources read.
  - Quantitative corrosion data (rates, mass gain, threshold temperatures) were not found. Corrosion entries are qualitative and come from Wikipedia and the safety data sheet.
  - 'Hazard classification differs by source: PubChem gives H228 (flammable solid) for 93.3 % of notifications, the Goodfellow foil page shows a flammable pictogram, and the Stanford Advanced Materials sheet gives no H statements. The Fisher Scientific and Glentham pages timed out or were not readable, and the UMN safety data sheet could not be downloaded.'
  - 'Space environment for the metal itself: none found. The NICT and Agiltron results are for amplifier hardware, not for erbium metal, and the radiation and thermal results are not entered as material properties.'
  - 'Production route: Wikipedia has a Production section that was not read in detail, so no process steps are described in the recipe.'
  - 'Media: no image with a usable licence was sourced in this run.'
  - Seven sources were read in this run, one short of the eight asked for. The two blocked suppliers and the UMN safety data sheet were the sources lost.
sources:
  usgs-rare-earths:
    title: 'Mineral Commodity Summaries 2026: Rare Earths (USGS)'
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-rare-earths.pdf
    year: 2026
    kind: report
    license: public domain (USGS)
  wikipedia-er:
    title: Erbium (Wikipedia)
    url: https://en.wikipedia.org/wiki/Erbium
    year: 2026
    kind: web
    license: CC BY-SA 4.0 (cited, not reproduced)
  pubchem-er:
    title: 'PubChem compound record: Erbium (CID 23980), including ECHA C&L Inventory classification'
    id: CAS 7440-52-0
    url: https://pubchem.ncbi.nlm.nih.gov/compound/23980
    kind: database
    license: PubChem (NCBI), public domain; sections attributed to ECHA and others
  sam-er-msds:
    title: 'Material Safety Data Sheet: Erbium Metal (Stanford Advanced Materials, 2012), copy hosted by Sputtertargets.net'
    url: https://www.sputtertargets.net/Public/pdf/erbium-msds.pdf
    year: 2012
    kind: datasheet
    license: supplier safety data sheet, cited not reproduced
  goodfellow-er-foil:
    title: Erbium foil light tight group (Goodfellow product datasheet, UK)
    url: https://www.goodfellow.com/uk/erbium-foil-light-tight-group
    kind: datasheet
    license: supplier web page, cited not reproduced
  nict-edfa-frontiers:
    title: 'Frontiers in Physics 2025: erbium-doped fibre amplifier for the CubeSOTA 6U CubeSat optical terminal (NICT)'
    url: https://www.frontiersin.org/journals/physics/articles/10.3389/fphy.2025.1542043/full
    year: 2025
    kind: paper
    license: open access, cited not reproduced
  agiltron-space-edfa:
    title: Agiltron space-qualified erbium/ytterbium small signal fibre amplifier (product page)
    url: https://agiltron.com/?p=22667
    kind: web
    license: vendor web page, cited not reproduced
license: CC-BY-4.0
updated: '2026-10-26'
review:
  status: draft
  method: assistant
  checked_values: 14
  unreachable: 3
  caveats: 6
  note: 'Values were read by an AI assistant on 2026-10-26 from the pages and PDFs named in each entry. Unreachable: American Elements erbium page (HTTP 403), Fisher Scientific erbium page (timeout), UMN erbium safety data sheet (download failed). Caveats: the density values differ by up to 0.06 g/cm3 (Wikipedia 9.065, safety data sheet 9.01) and the boiling points by 5 °C; hardness values are ranges; the USGS supply figures are for the whole rare-earth group, not erbium; the hazard classifications differ between sources; corrosion entries are qualitative.'
story:
  risk_groups:
    - title: For people
      lead: The hazard is in fine metal and dust. Sources disagree on the classification, and the toxicology is incompletely studied.
      level: 1
      verdict: Form-dependent
      points:
        - label: Fine metal
          line: PubChem lists H228, flammable solid, with signal word Danger, for 93.3 % of reports. The Goodfellow foil sheet shows a flammable pictogram.
        - label: Dust
          line: The Stanford Advanced Materials sheet says dust may cause asthma attacks and lung damage, including lung granulomas. It also says the toxicology has not been thoroughly investigated.
        - label: Acid
          line: The same sheet says the metal reacts with dilute acids and emits flammable and explosive hydrogen gas.
    - title: If it fails
      lead: 'The sources give three failure routes: a fire in fine metal, hydrogen release in acid, and slow tarnish in moist air.'
      points:
        - label: Fire in fines
          line: PubChem quotes Hawley that fine metal is flammable.
        - label: Acid
          line: Hydrogen release on contact with dilute acids is flammable and explosive (Stanford Advanced Materials).
        - label: Moist air and water
          line: Wikipedia says erbium tarnishes slowly in moist air and reacts quite quickly with hot water.
    - title: Handling and storage
      points:
        - label: Store dry
          line: Keep in a cool, dry area in a tightly sealed container, and handle in a dry, controlled atmosphere (Stanford Advanced Materials).
        - label: Fire
          line: Use Class D or another metal extinguishing agent, and do not use water (Stanford Advanced Materials).
  why: Erbium is a rare earth metal whose main value is in optics. Its atoms emit and amplify light in silica fibre, which makes erbium-doped fibre amplifiers central to long-distance optical links (Wikipedia). It is also the source of a 2940 nm laser emission used in medical lasers (Wikipedia). Its supply is concentrated, since the USGS reports China as the source of 71 % of U.S. imports of rare-earth compounds and metals in 2021 to 2024, and China added erbium to its export controls in October.
  uses:
    - where: Optical fibre amplifiers
      line: Erbium-doped silica fibre is the active element of fibre amplifiers used in optical links (Wikipedia).
    - where: CubeSat optical terminal
      line: NICT reports a compact two-stage erbium-doped amplifier for the 6U CubeSOTA CubeSat in low Earth orbit, with an output above 2 W (Frontiers in Physics 2025).
    - where: Satellite links
      line: Agiltron sells a vacuum-rated erbium/ytterbium amplifier for satellite communication, designed for over 10 years of reliable operation (product page).
    - where: Medical lasers
      line: Wikipedia says medical uses of erbium utilise the erbium ion's 2940 nm emission, as in Er:YAG lasers.
  can_do:
    - label: Amplify light
      value: Erbium-doped fibre
      line: Erbium-doped silica fibre is the active element of fibre amplifiers (Wikipedia).
    - label: Weight
      value: 9.065 g/cm3
      benchmark: density
      line: Density is 9.065 g/cm3 at 20 °C in the Wikipedia infobox, and 9.051 g/cm3 at 20 °C for the Goodfellow foil.
    - label: Melting
      value: 1529 °C
      benchmark: melting_point
      line: Melting point is 1529 °C in the Wikipedia infobox, the safety data sheet and the Goodfellow foil datasheet.
    - label: Carry heat
      value: 14.5 W/(m⋅K)
      benchmark: thermal_conductivity
      line: Thermal conductivity is 14.5 W/(m⋅K), with no temperature given (Wikipedia).
    - label: Stiffness
      value: 69.9 GPa
      benchmark: elastic_modulus
      line: Young's modulus is 69.9 GPa (Wikipedia infobox).
  compare: Erbium is a rare earth metal of moderate density, 9.065 g/cm3 at 20 °C, and it melts at 1529 °C (Wikipedia). Its Young's modulus is 69.9 GPa (Wikipedia). It is used for its optical behaviour in fibre amplifiers, not for structural strength, so the strength and melting rows should be read as basic metal data rather than as a design comparison.
  compare_rows:
    - label: Density
      benchmark: density
    - label: Melting point
      benchmark: melting_point
    - label: Thermal conductivity
      benchmark: thermal_conductivity
  recipe:
    line: Erbium is a single-element metal (Er) with a hexagonal close-packed structure at room temperature (Wikipedia). Commercial pieces are made from rare earth ores, mainly xenotime and euxenite (Wikipedia). The Wikipedia production section was not read in detail, so no process steps are given here.
    parts:
      - name: Erbium
        symbol: Er
        atoms: 1
        atomic_weight: 167.259
        role: The whole material. The standard atomic weight is 167.259 in the Wikipedia infobox. Goodfellow foil is 99 % (2N) purity.
  handling:
    - Store in a cool, dry area in a tightly sealed container (Stanford Advanced Materials).
    - Handle in a dry, controlled atmosphere and wear a NIOSH approved respirator, rubber gloves and safety glasses (Stanford Advanced Materials).
    - Use Class D or another metal extinguishing agent on fires, and do not use water (Stanford Advanced Materials).
  good_for:
    - 'Optical amplification: erbium-doped silica fibre amplifies light in optical links (Wikipedia).'
    - 'Compact space hardware: a 2 W erbium-doped CubeSat amplifier is designed for low Earth orbit (NICT).'
    - 'Medical lasers: the 2940 nm erbium emission is used in Er:YAG lasers (Wikipedia).'
  watch_out:
    - Fine metal is a flammable solid (PubChem H228), and the metal releases hydrogen on contact with acid.
    - Sources disagree on the classification, and the metal's toxicology is incompletely studied (Stanford Advanced Materials).
    - Supply is concentrated in China, which added erbium to its export controls in October (USGS).
    - The supply shares are for the whole rare-earth group, so no erbium-specific production figure is available.
  verdict: Erbium is a rare earth metal whose value lies in optical amplification, and its density of 9.065 g/cm3 and melting point of 1529 °C are well documented. Its flammability in fine form and its reaction with acid and hot water need the handling steps above. Its supply data are for the rare-earth group rather than erbium alone, and the hardness and toxicology data are thinner than the physical values.