spore: profile
id: holmium
spore_version: 0.2
family: rare-earth-metals
name: Holmium
abbreviation: Ho
role: magnetic pole-piece material and neutron absorber
category: metals
type: heavy-metals
summary: |
  Holmium is the element Ho (atomic number 67), a soft, malleable, silvery lanthanide metal. Wikipedia gives a density of 8.795 g/cm3 at 20 °C and a melting point of 1461 °C, while Goodfellow and three safety data sheets print 1474 °C. It is found with other rare earths in monazite and ion-adsorption clays, and its crust abundance is 1.3 mg/kg. Holmium has the highest magnetic moment of any naturally occurring element (10.6 μB), which is why it is used for the pole pieces of the strongest static magnets. It also absorbs neutrons strongly and serves as a burnable poison in some reactors. The metal tarnishes in moist air and reacts with water to release a flammable gas, and its powder is a flammable solid, so it needs dry, inert handling.
best_for: Strong magnetic pole pieces and neutron absorption, where its 10.6 μB magnetic moment and strong neutron capture matter (Wikipedia, Goodfellow)
weakest_at: Fine powder that can ignite, and metal that releases flammable hydrogen on contact with water (Angstrom SDS, Prochem SDS)
identity:
  formula: Ho (element, atomic number 67); unalloyed metal sold as powder, foil, pieces and sputtering targets
  cas: 7440-60-0
  crystal_system: hexagonal close-packed (hcp), Pearson symbol hP2
  source: wikipedia-ho
  where: Infobox, rows CAS Number and Crystal structure; lattice constants a = 357.80 pm and c = 561.77 pm at 20 °C. EC number 231-169-0 is printed in the Angstrom SDS, Section 1.
tags:
  environments: []
  applications:
    - radiation-shielding
    - electronics-and-chips
    - optics-and-cameras
properties:
  - benchmark: density
    label: Density, holmium
    value: 8.795
    unit: g/cm3
    scope: material
    conditions:
      temperature: 20 °C
      unit_in_source: 8.795 g/cm3
    method: Value printed in the Wikipedia infobox
    status: ground
    source: wikipedia-ho
    where: Infobox, row Density (at 20° C) 8.795 g/cm3
  - benchmark: density
    label: Density of solid, holmium (WebElements)
    value: 8795
    unit: kg/m3
    scope: material
    conditions:
      temperature: not stated
      unit_in_source: 8795 kg m-3
    method: Value printed on the WebElements physical-properties page
    status: ground
    source: webelements-ho
    where: Density properties, row Density of solid 8795 kg m-3
  - benchmark: melting_point
    label: Melting point, holmium (Wikipedia)
    value: 1461
    unit: °C
    scope: material
    conditions:
      pressure: not stated
      unit_in_source: 1734 K (1461 °C, 2662 °F)
    method: Value printed in the Wikipedia infobox
    status: ground
    note: Goodfellow and the Angstrom, Prochem and SAM SDS sheets print 1474 °C, and the Wikipedia value is 13 °C lower. Both are kept.
    source: wikipedia-ho
    where: Infobox, row Melting point, 1734 K (1461 °C, 2662 °F)
  - benchmark: melting_point
    label: Melting point, holmium (Goodfellow)
    value: 1474
    unit: °C
    scope: material
    conditions:
      pressure: not stated
      purity: not stated
    method: Value printed in the Goodfellow material information page
    status: ground
    source: goodfellow-ho
    where: Material information text, paragraph beginning 'Holmium crystallizes', melting point of 1474 °C
  - benchmark: melting_point
    label: Melting point, holmium powder (Angstrom SDS)
    value: 1474
    unit: °C
    scope: material
    conditions:
      pressure: not stated
    method: Value printed in a supplier safety data sheet, Section 9
    status: ground
    source: angstrom-ho-sds
    where: Section 9 Physical and Chemical Properties, row Melting Point 1474°C
  - benchmark: boiling_point
    label: Boiling point, holmium (Wikipedia)
    value: 2600
    unit: °C
    scope: material
    conditions:
      pressure: not stated
      unit_in_source: 2873 K (2600 °C, 4712 °F)
    method: Value printed in the Wikipedia infobox
    status: ground
    note: The four sources differ widely (2600, 2695, 2700 and 2965 °C), so each value is entered with its source.
    source: wikipedia-ho
    where: Infobox, row Boiling point, 2873 K (2600 °C, 4712 °F)
  - benchmark: boiling_point
    label: Boiling point, holmium powder (Prochem SDS)
    value: 2695
    unit: °C
    scope: material
    conditions:
      pressure: not stated
    method: Value printed in a supplier safety data sheet, Section 9
    status: ground
    source: prochem-ho-sds
    where: Section 9 Physical and Chemical Properties, row BOILING POINT 2695° C
  - benchmark: boiling_point
    label: Boiling point, holmium (Angstrom SDS)
    value: 2700
    unit: °C
    scope: material
    conditions:
      pressure: not stated
    method: Value printed in a supplier safety data sheet, Section 9
    status: ground
    source: angstrom-ho-sds
    where: Section 9 Physical and Chemical Properties, row Boiling Point 2700°C
  - benchmark: boiling_point
    label: Boiling point, holmium (SAM SDS)
    value: 2965
    unit: °C
    scope: material
    conditions:
      pressure: not stated
    method: Value printed in a 2012 Stanford Advanced Materials safety data sheet, Section III
    status: ground
    source: sam-ho-sds
    where: Section III Physical/Chemical Characteristics, row Boiling Point 2965°C
  - benchmark: specific_heat
    label: Specific heat capacity, holmium
    value: 164.615
    unit: J/(kg·K)
    scope: material
    conditions:
      temperature: not stated in the infobox
    method: Value printed in the Wikipedia infobox
    status: ground
    source: wikipedia-ho
    where: Infobox, row Specific heat capacity 164.615 J/(kg·K); molar heat capacity 27.15 J/(mol·K) is printed in the same table
  - benchmark: cte
    label: Coefficient of thermal expansion, holmium (Wikipedia)
    value: 11.2
    unit: ppm/K
    scope: material
    conditions:
      temperature: room temperature
      material_condition: polycrystalline
      unit_in_source: 11.2 µm/(m⋅K)
    method: Value printed in the Wikipedia infobox
    status: ground
    source: wikipedia-ho
    where: Infobox, row Thermal expansion, poly 11.2 µm/(m⋅K) at room temperature
  - benchmark: cte
    label: Coefficient of linear thermal expansion, holmium (WebElements)
    value: 11.2
    unit: ppm/K
    scope: material
    conditions:
      temperature: not stated
      unit_in_source: 11.2 × 10-6 K-1
    method: Value printed on the WebElements physical-properties page
    status: ground
    source: webelements-ho
    where: Heat and conduction, Coefficient of linear thermal expansion 11.2 × 10-6 K-1
  - benchmark: thermal_conductivity
    label: Thermal conductivity, holmium (Wikipedia)
    value: 16.2
    unit: W/(m·K)
    scope: material
    conditions:
      temperature: not stated in the infobox
    method: Value printed in the Wikipedia infobox
    status: ground
    source: wikipedia-ho
    where: Infobox, row Thermal conductivity 16.2 W/(m⋅K)
  - benchmark: thermal_conductivity
    label: Thermal conductivity, holmium (WebElements)
    value: 16
    unit: W/(m·K)
    scope: material
    conditions:
      temperature: not stated
      unit_in_source: 16 W m-1 K-1
    method: Value printed on the WebElements physical-properties page
    status: ground
    source: webelements-ho
    where: Heat and conduction, Thermal conductivity 16 W m-1 K-1
  - benchmark: electrical_resistivity
    label: Electrical resistivity, holmium, polycrystalline
    value: 814
    unit: nΩ·m
    scope: material
    conditions:
      temperature: room temperature
      material_condition: polycrystalline
    method: Value printed in the Wikipedia infobox
    status: ground
    source: wikipedia-ho
    where: Infobox, row Electrical resistivity, poly 814 nΩ⋅m at room temperature
  - benchmark: elastic_modulus
    label: Young's modulus, holmium (Wikipedia)
    value: 64.8
    unit: GPa
    scope: material
    conditions:
      temperature: not stated in the infobox
    method: Value printed in the Wikipedia infobox
    status: ground
    source: wikipedia-ho
    where: Infobox, row Young's modulus 64.8 GPa
  - benchmark: elastic_modulus
    label: Young's modulus, holmium (WebElements)
    value: 65
    unit: GPa
    scope: material
    conditions:
      temperature: not stated
    method: Value printed on the WebElements physical-properties page
    status: ground
    source: webelements-ho
    where: Elastic properties, Young's modulus 65 GPa
  - benchmark: shear_modulus
    label: Shear modulus (rigidity), holmium (Wikipedia)
    value: 26.3
    unit: GPa
    scope: material
    conditions:
      temperature: not stated in the infobox
    method: Value printed in the Wikipedia infobox
    status: ground
    source: wikipedia-ho
    where: Infobox, row Shear modulus 26.3 GPa
  - benchmark: shear_modulus
    label: Rigidity modulus, holmium (WebElements)
    value: 26
    unit: GPa
    scope: material
    conditions:
      temperature: not stated
    method: Value printed on the WebElements physical-properties page
    status: ground
    source: webelements-ho
    where: Elastic properties, Rigidity modulus 26 GPa
  - benchmark: bulk_modulus
    label: Bulk modulus, holmium
    value: 40.2
    unit: GPa
    scope: material
    conditions:
      temperature: not stated in the infobox
    method: Value printed in the Wikipedia infobox
    status: ground
    source: wikipedia-ho
    where: Infobox, row Bulk modulus 40.2 GPa
  - benchmark: poissons_ratio
    label: Poisson's ratio, holmium (Wikipedia)
    value: 0.231
    unit: '-'
    scope: material
    conditions:
      temperature: not stated in the infobox
    method: Value printed in the Wikipedia infobox
    status: ground
    source: wikipedia-ho
    where: Infobox, row Poisson ratio 0.231
  - benchmark: poissons_ratio
    label: Poisson's ratio, holmium (WebElements)
    value: 0.23
    unit: '-'
    scope: material
    conditions:
      temperature: not stated
    method: Value printed on the WebElements physical-properties page
    status: ground
    source: webelements-ho
    where: Elastic properties, Poisson's ratio 0.23 (no units)
  - benchmark: vickers_hardness
    label: Vickers hardness range, holmium
    value: 410
    value_high: 600
    bound: range
    unit: MPa
    scope: material
    conditions:
      temperature: not stated in the infobox
      note_on_range: the infobox gives a range, not a single test value
    method: Range printed in the Wikipedia infobox
    status: ground
    note: No canonical name exists for hardness, so vickers_hardness is a new name and is listed in gaps. The range is given by Wikipedia without test conditions.
    source: wikipedia-ho
    where: Infobox, row Vickers hardness 410–600 MPa
  - benchmark: vickers_hardness
    label: Vickers hardness, holmium (WebElements)
    value: 481
    unit: MPa
    scope: material
    conditions:
      temperature: not stated
    method: Value printed on the WebElements physical-properties page, given as MN m-2 (equal to MPa)
    status: ground
    note: No canonical name exists for hardness, so vickers_hardness is a new name and is listed in gaps.
    source: webelements-ho
    where: Hardnesses, row Vickers hardness 481 MN m-2
  - benchmark: curie_temperature
    label: Ferromagnetic transition, holmium
    value: 19
    unit: K
    scope: material
    conditions:
      transition: ferromagnetic below this temperature
      pressure: not stated
    method: Value printed in the Wikipedia text on magnetism
    status: ground
    note: Goodfellow gives ferromagnetic below 20 K, so the two sources differ by 1 K. Wikipedia's value is used.
    source: wikipedia-ho
    where: Section Magnetism paragraph beginning 'Holmium, like all of the lanthanides, is paramagnetic'
  - benchmark: neel_temperature
    label: Paramagnetic to antiferromagnetic transition, holmium
    value: 133
    unit: K
    scope: material
    conditions:
      transition: paramagnetic above 133 K; antiferromagnetic between 20 and 133 K
      citation_in_source: Rhodes et al., 1958
    method: Value printed in the Goodfellow material information page, which cites a 1958 paper
    status: ground
    note: No canonical name exists for this transition, so neel_temperature is a new name and is listed in gaps. Goodfellow is the only source read for this value.
    source: goodfellow-ho
    where: Material information text, paragraph on magnetic behaviour
  - benchmark: thermal_neutron_cross_section
    label: Neutron absorption cross-section, holmium
    value: 64
    unit: barn
    scope: material
    conditions:
      neutron: not stated
      unit_in_source: about 64 barns
    method: Value printed on the Goodfellow material information page under applications
    status: ground
    note: The page gives no isotope or temperature. No canonical name exists, so thermal_neutron_cross_section is a new name and is listed in gaps.
    source: goodfellow-ho
    where: Applications and Advantages paragraph, neutron absorption cross-section (~64 barns)
corrosion:
  - environment: Dry air at room temperature
    headline: Holmium is fairly corrosion-resistant and stable in dry air at room temperature.
    effect: Wikipedia says the metal is fairly corrosion-resistant and chemically stable in dry air at standard temperature and pressure, and that it tarnishes slowly in air to form a yellowish oxide layer.
    rating: low
    conditions:
      temperature: standard temperature and pressure
      atmosphere: dry air
    source: wikipedia-ho
    where: Chemical properties section, paragraphs on air and oxidation
  - environment: Moist air and heating in air
    headline: Holmium oxidizes quickly in moist air and at higher temperatures, and burns when heated.
    effect: Wikipedia says that in moist air and at higher temperatures holmium quickly oxidizes to a yellowish oxide, and that it burns readily to form holmium(III) oxide. No corrosion rate figure is given in the sources read.
    rating: severe
    conditions:
      atmosphere: moist air
      temperature: higher temperatures, not quantified
    source: wikipedia-ho
    where: Chemical properties section, paragraphs on tarnishing and on moist air
  - environment: Cold and hot water
    headline: Holmium reacts slowly with cold water and quickly with hot water.
    effect: Wikipedia says holmium reacts slowly with cold water and quickly with hot water to form holmium(III) hydroxide. The Angstrom and Prochem SDS sheets say that contact with water releases a flammable gas that may ignite spontaneously (H260).
    rating: severe
    conditions:
      temperature: cold and hot water
      form: metal, powder and pieces
    source: wikipedia-ho
    where: Chemical properties section, paragraph on water
  - environment: Dilute and strong acids
    headline: Holmium dissolves in acids.
    effect: Wikipedia says holmium dissolves in acids. The SAM SDS lists strong acids as incompatible, and the Prochem SDS lists mineral acids.
    rating: moderate
    conditions:
      acid: not named
      temperature: not stated
    source: wikipedia-ho
    where: Chemical properties section, paragraph on holmium(III) compounds, sentence 'Holmium dissolves in acids'
  - environment: Halogens and strong oxidizers
    headline: Holmium is incompatible with halogens and oxidizing agents.
    effect: The SAM SDS lists strong acids, oxidizing agents, acid chlorides and halogens as incompatible. The Prochem SDS lists strong oxidizers, oxygen and halogens as incompatible.
    rating: moderate
    conditions:
      atmosphere: halogen or oxidizer contact
    source: sam-ho-sds
    where: Section V Reactivity Data, Incompatibility
risks:
  hazards:
    - text: 'PubChem GHS summary: H228 (flammable solid) in 84% of notified classifications, signal word Danger. The record says the substance does not meet GHS hazard criteria in 4 of 50 company reports.'
      ghs:
        - H228
      source: pubchem-ho
      where: Safety and Hazards, GHS Classification (CID 23988)
    - text: 'Angstrom Sciences SDS (rev. 07/22/15): signal word Danger. H228 flammable solid, and H260 in contact with water releases flammable gases which may ignite spontaneously. Flammability is listed as non-flammable except as powder.'
      ghs:
        - H228
        - H260
      source: angstrom-ho-sds
      where: Section 2 Hazard Identification; Section 5 Fire Fighting Measures
    - text: 'Prochem powder SDS (product 1966, prepared 04/15, hosted by Purdue PRIMELab): H228 and H260 with the same precautionary phrases. NFPA flammability 3 and reactivity 2.'
      ghs:
        - H228
        - H260
      source: prochem-ho-sds
      where: Section 2 Hazards Identification; HMIS and NFPA ratings
    - text: The shipping class differs between the SDS sheets. Angstrom lists packing group II for UN3089 (powder) and UN3178 (pieces), both Class 4.1. Prochem lists UN3089 Class 4.1 with packing group III for the powder. Check the classification of the lot being shipped.
      ghs: []
      source: angstrom-ho-sds
      where: Section 14 Transport Information; compare Prochem SDS Section 14
    - text: Stanford Advanced Materials SDS (rev. 2012) gives no GHS statements. It says the complete health hazards have not been fully examined and lists low inhalation and oral toxicity as possible.
      ghs: []
      source: sam-ho-sds
      where: Section VI Health Hazard Data
  failure_risks:
    - mode: Fire in powder, fines and chips
      trigger: Holmium powder or fines exposed to heat, sparks, moisture or air, or to dust clouds
      consequence: The powder is a flammable solid (H228, Angstrom and Prochem SDS). The SAM SDS lists dusting conditions, electric arcs and sparks as conditions to avoid. A fire on the metal must be fought with special powder or Class D agents, not water.
      severity: critical
      source: angstrom-ho-sds
      where: Angstrom Section 2 (H228) and Section 5; SAM Section V Conditions to Avoid
    - mode: Hydrogen release on contact with water
      trigger: Metal or powder in contact with water or moisture
      consequence: The Angstrom and Prochem SDS say that contact with water releases a flammable gas that may ignite spontaneously (H260). Wikipedia says holmium reacts quickly with hot water. Water also feeds a fire on the metal.
      severity: critical
      source: angstrom-ho-sds
      where: Section 2 hazard statement H260; Section 9 Water Solubility; Section 10 Reactivity
    - mode: Oxide tarnish in moist air
      trigger: Exposure to moist air, especially at higher temperature
      consequence: Wikipedia says holmium quickly oxidizes in moist air and at higher temperatures to a yellowish oxide. The sources read give no rate of loss of metal.
      severity: moderate
      source: wikipedia-ho
      where: Chemical properties section, paragraph on moist air
    - mode: Reaction with halogens, acids and oxidizers
      trigger: Contact with halogens, strong acids, acid chlorides or oxidizing agents
      consequence: The SAM and Prochem SDS sheets list these as incompatible materials, and Wikipedia says holmium dissolves in acids.
      severity: moderate
      source: sam-ho-sds
      where: Section V Reactivity Data, Incompatibility; Prochem Section 10
  side_effects:
    - text: The Angstrom SDS lists chronic effects of lanthanons, including delayed blood clotting that can lead to hemorrhages and liver damage, plus sensitivity to heat and itching. The SDS gives no specific toxicity data for holmium.
      affects: People with repeated or long-term exposure to lanthanide dust
      source: angstrom-ho-sds
      where: Section 11 Toxicological Information, Chronic
  handling:
    - text: 'Angstrom SDS: handle under dry protective gas, protect from moisture, store in a dry place in a closed container, and do not raise dust (Section 2 precautionary statements P231+P232 and P402+P404; Section 6).'
      source: angstrom-ho-sds
      where: Sections 2, 6 and 7
    - text: 'Prochem SDS: store under inert gas in a cool, dry, well-ventilated area, away from water, air, moisture, oxidizing agents and acid chlorides. Keep containers closed.'
      source: prochem-ho-sds
      where: Section 7 Handling and Storage
    - text: 'Fire: the Angstrom and Prochem SDS say to use special powder for metal fires and not water. The SAM SDS says to use dry chemical or a Class D extinguisher and not water.'
      source: sam-ho-sds
      where: Section IV Fire and Explosion Hazard Data; Angstrom Section 5; Prochem Section 5
    - text: Wear nitrile or rubber gloves, goggles or a face shield, and an approved respirator with local exhaust ventilation where dust forms (Prochem SDS).
      source: prochem-ho-sds
      where: Section 8 Exposure Controls and Personal Protection
    - text: Clean up spills with a HEPA-filter vacuum in a closed container, taking care not to raise dust (Angstrom SDS; SAM SDS).
      source: angstrom-ho-sds
      where: Section 6 Accidental Release Measures
  mitigations: []
uses:
  - application: radiation-shielding
    device: Burnable poison (neutron absorber) in nuclear reactors
    example: Wikipedia says that because holmium absorbs nuclear fission-bred neutrons strongly, it is used as a burnable poison to regulate nuclear reactors. The Goodfellow page also lists nuclear control rods among its applications.
    source: wikipedia-ho
    where: Uses section, paragraph on nuclear reactors; Goodfellow Applications and Advantages
  - application: electronics-and-chips
    device: Pole pieces of the strongest static magnets (magnetic flux concentrators)
    example: Wikipedia says holmium has the highest magnetic permeability and magnetic saturation of any element and is used for the pole pieces of the strongest static magnets. The application list has no magnets category, so this is filed under electronics-and-chips.
    source: wikipedia-ho
    where: Physical properties section, paragraph beginning 'Holmium has the highest magnetic permeability'
  - application: optics-and-cameras
    device: Holmium oxide wavelength and absorbance reference in spectrophotometers
    example: Wikipedia says glass and solutions containing holmium oxide have sharp optical absorption peaks from 200 to 900 nm and are used as calibration standards for optical spectrophotometers. This is the oxide, not the metal.
    source: wikipedia-ho
    where: Uses section, paragraph on calibration standards
  - application: optics-and-cameras
    device: Holmium-doped solid-state lasers at 2.1 µm (medical and LIDAR)
    example: The Goodfellow page says holmium-doped materials are used in solid-state lasers operating at 2.1 µm for medical and LIDAR systems. The page gives no source or test data for this claim, and it is a doped laser material, not the metal.
    source: goodfellow-ho
    where: Applications and Advantages paragraph
supply:
  - subject: Rare earths (holmium is not reported separately by USGS)
    abundance: 1.3 mg/kg in the Earth's crust (Wikipedia, citing the CRC Handbook, 1.3 parts per million)
    producers:
      - country: China
        share_percent: 69.2
        year: 2025
      - country: United States
        share_percent: 13.1
        year: 2025
      - country: Australia
        share_percent: 7.4
        year: 2025
      - country: Burma
        share_percent: 5.6
        year: 2025
    critical_lists: []
    recycling: 'USGS: limited quantities of rare earths were recovered from batteries, permanent magnets and fluorescent lamps.'
    substitutes:
      - 'USGS: substitutes are available for many rare-earth applications but generally are less effective.'
    source: usgs-ree-2026
    where: 'World Mine Production table, 2025 (world total 390,000 t, rounded; shares calculated by Space Mushroom from China 270,000, United States 51,000, Australia 29,000 and Burma 22,000). Reserves: China 44,000,000 t. Recycling and Substitutes sections. Abundance: Wikipedia Occurrence section.'
  - subject: Rare-earth compounds and metals imported into the United States
    producers:
      - country: China
        share_percent: 71
        year: 2024
      - country: Malaysia
        share_percent: 13
        year: 2024
      - country: Japan
        share_percent: 5
        year: 2024
      - country: Estonia
        share_percent: 5
        year: 2024
    critical_lists: []
    recycling: ''
    substitutes: []
    source: usgs-ree-2026
    where: Import Sources (2021–24) paragraph; the year column shows the end of the 2021 to 2024 range. Net import reliance for compounds and metals in 2025e is 67 %, from the Salient Statistics table.
  - subject: Export controls that name holmium
    producers: []
    critical_lists: []
    recycling: ''
    substitutes: []
    source: usgs-ree-2026
    where: 'Events, Trends, and Issues: in October 2025 China expanded its rare-earth export controls to include europium, holmium, erbium, thulium and ytterbium. In November it suspended the October controls for one year, and the April 2025 controls remained in effect.'
media: []
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: Holmium'
    type: database
    url: https://en.wikipedia.org/wiki/Holmium
    year: 2026
  - title: PubChem compound record for holmium (CID 23988), including GHS classification
    type: database
    url: https://pubchem.ncbi.nlm.nih.gov/compound/23988
    year: 2026
  - title: 'WebElements: Holmium, physical properties (University of Sheffield)'
    type: datasheet
    url: https://winter.group.shef.ac.uk/webelements/holmium/physics.html
    year: 2026
  - title: 'Goodfellow: Holmium metal, material information (USA page)'
    type: datasheet
    url: https://www.goodfellow.com/usa/resources/holmium-metal-material-information/
    year: 2026
  - title: 'Safety data sheet: Holmium, Angstrom Sciences (rev. 07/22/15)'
    type: sds
    url: https://angstromsciences.com/wp-content/uploads/files/SDS/Holmium.pdf
    year: 2015
  - title: 'Safety data sheet: Holmium powder, Prochem product 1966 (prepared 04/15), copy hosted by Purdue PRIMELab'
    type: sds
    url: https://www.physics.purdue.edu/primelab/safety/MSDS/SDS/holmium%20powder%20%20-%20Prochem.pdf
    year: 2015
  - title: 'Material safety data sheet: Holmium, Stanford Advanced Materials (rev. 2012), copy hosted by sputtertargets.net'
    type: sds
    url: https://www.sputtertargets.net/Public/pdf/holmium-msds.pdf
    year: 2012
  - title: 'NIST: Atomic weights and isotopic compositions for all elements (holmium entry)'
    type: database
    url: https://physics.nist.gov/cgi-bin/Compositions/stand_alone.pl?ele=Ho&all=all&ascii=html
    year: 2026
gaps:
  - Holmium is not reported separately by USGS, so the producer shares above are for all rare earths and not for holmium. World output of holmium metal was not found in an opened source.
  - 'Critical-mineral listing: the USGS 2025 critical minerals list and the EU critical raw materials list were not opened for holmium, so critical_lists is empty.'
  - 'Space flight of holmium metal: no flight, vacuum, radiation or thermal-cycling test of holmium metal was found in the sources read. The environments tag is empty for that reason, and no environment is claimed.'
  - 'Media: no image was fetched or credited in this run, so media is empty.'
  - 'Melting point: Wikipedia gives 1461 °C, while Goodfellow and the Angstrom and Prochem SDS sheets give 1474 °C. Both values are entered with their sources. The SAM SDS also gives 1474 °C.'
  - 'Boiling point: Wikipedia gives 2600 °C, Prochem 2695 °C, Angstrom 2700 °C and SAM 2965 °C. The spread is wide, so all four are entered and none is preferred.'
  - 'Magnetic transitions: Wikipedia gives ferromagnetic below 19 K, and Goodfellow gives 20 K. The 133 K paramagnetic to antiferromagnetic transition is only in the Goodfellow page, and it is entered under the new name neel_temperature.'
  - 'Neutron cross-section: the ~64 barn figure comes from the Goodfellow page only, with no isotope or temperature. It is entered under the new name thermal_neutron_cross_section.'
  - 'Hardness: Vickers hardness is entered under the new name vickers_hardness, because the property file has no canonical name for hardness. The Brinell hardness (746 MN m-2 in WebElements, 500 to 1250 MPa in Wikipedia) is not entered for the same reason.'
  - Speed of sound (2760 m/s, WebElements and Wikipedia) is not entered, because the property file has no canonical name for it.
  - Atomic weight is entered in recipe.parts from the NIST abridged value of 164.93033(2). The Wikipedia value is 164.930329(5).
  - 'Purity: the Goodfellow page does not state a purity, and no certificate of analysis was opened. Values are for unspecified holmium metal.'
  - 'Hazard data differ: PubChem shows H228 for most notifications, Angstrom and Prochem add H260, and the SAM 2012 sheet has no GHS statements. The packing group for UN3089 differs between Angstrom (II) and Prochem (III).'
  - Corrosion data are qualitative (Wikipedia and the SDS sheets). No measured weight-gain or corrosion-rate figure for holmium in air or water was found.
  - 'Not opened: the American Elements holmium page (not fetched), and no Apollo Scientific or Lesker holmium SDS was found in the search.'
  - 'Uses: the space-relevant use is none. The laser use rests on the Goodfellow page alone, and no peer-reviewed laser paper was opened in this run.'
sources:
  wikipedia-ho:
    title: Holmium (Wikipedia)
    url: https://en.wikipedia.org/wiki/Holmium
    year: 2026
    kind: web
    license: CC BY-SA 4.0 (cited, not reproduced)
  webelements-ho:
    title: 'WebElements: Holmium, physical properties (University of Sheffield)'
    url: https://winter.group.shef.ac.uk/webelements/holmium/physics.html
    year: 2026
    kind: database
    license: WebElements, cited not reproduced
  goodfellow-ho:
    title: 'Goodfellow: Holmium metal, material information (USA page)'
    url: https://www.goodfellow.com/usa/resources/holmium-metal-material-information/
    year: 2026
    kind: datasheet
    license: supplier web page (cited, not reproduced)
  pubchem-ho:
    title: 'PubChem compound record: Holmium (CID 23988), including ECHA C&L Inventory classification'
    id: CID 23988; CAS 7440-60-0
    url: https://pubchem.ncbi.nlm.nih.gov/compound/23988
    year: 2026
    kind: database
    license: PubChem (NCBI), public domain; sections attributed to ECHA and others
  usgs-ree-2026:
    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)
  angstrom-ho-sds:
    title: 'Safety data sheet: Holmium (Angstrom Sciences, rev. 07/22/15)'
    id: CAS 7440-60-0; EC 231-169-0
    url: https://angstromsciences.com/wp-content/uploads/files/SDS/Holmium.pdf
    year: 2015
    kind: datasheet
    license: supplier safety data sheet, cited not reproduced
  prochem-ho-sds:
    title: 'Safety data sheet: Holmium powder (Prochem, product 1966, prepared 04/15; copy hosted by Purdue PRIMELab)'
    id: CAS 7440-60-0
    url: https://www.physics.purdue.edu/primelab/safety/MSDS/SDS/holmium%20powder%20%20-%20Prochem.pdf
    year: 2015
    kind: datasheet
    license: supplier safety data sheet, cited not reproduced
  sam-ho-sds:
    title: 'Material safety data sheet: Holmium (Stanford Advanced Materials, rev. 2012; copy hosted by sputtertargets.net)'
    id: CAS 7440-60-0
    url: https://www.sputtertargets.net/Public/pdf/holmium-msds.pdf
    year: 2012
    kind: datasheet
    license: supplier safety data sheet, cited not reproduced
  nist-atomic-weights:
    title: 'NIST: Atomic weights and isotopic compositions for all elements (holmium)'
    url: https://physics.nist.gov/cgi-bin/Compositions/stand_alone.pl?ele=Ho&all=all&ascii=html
    year: 2026
    kind: database
    license: public domain (NIST)
license: CC-BY-4.0
updated: '2026-10-26'
review:
  status: draft
  method: assistant
  checked_values: 27
  unreachable: 0
  caveats: 6
  note: 'Read by an AI assistant on 2026-10-26 from the pages and PDFs named in each entry. Caveats: most physical values come from Wikipedia and WebElements; the melting and boiling points differ between sources; the magnetic transition temperatures and the neutron cross-section are from one source each; the hazard classes and the packing group differ between the SDS sheets; supply shares are for all rare earths, not holmium.'
story:
  risk_groups:
    - title: For people
      lead: The hazard is in the metal's form. The sources read give little toxicity data for solid holmium, but powder and fines are flammable and the SDS sheets report possible irritation and chronic lanthanide effects.
      level: 1
      verdict: Form-dependent
      points:
        - label: Powder and fines
          line: The Angstrom and Prochem SDS sheets classify the powder as a flammable solid (H228) with a water hazard (H260), and the signal word is Danger.
        - label: Water
          line: Contact with water releases a flammable gas that may ignite spontaneously (H260, Angstrom and Prochem SDS).
        - label: Toxicity
          line: The SAM SDS says the complete health hazards have not been fully examined but lists low inhalation and oral toxicity as possible. The Angstrom SDS lists chronic lanthanide effects, including delayed blood clotting and liver damage.
    - title: If it fails
      lead: 'The sources give four failure routes: a fire in powder or fines, hydrogen release on contact with water, oxide tarnishing in moist air, and reaction with halogens, acids and oxidizers.'
      points:
        - label: Fire
          line: A fire in fines needs special powder for metal fires or a Class D agent. Water must not be used on the metal (Angstrom, Prochem and SAM SDS).
        - label: Moist air
          line: Holmium quickly oxidizes in moist air and at higher temperature, forming a yellowish oxide layer (Wikipedia).
        - label: Halogens and acids
          line: The SAM and Prochem SDS list halogens, strong acids and oxidizers as incompatible, and Wikipedia says holmium dissolves in acids.
    - title: Handling and storage
      points:
        - label: Keep it dry
          line: Handle under dry protective gas and store under inert gas in a dry, closed container, away from moisture, oxidizers and acid chlorides (Angstrom and Prochem SDS).
        - label: Fire agents
          line: Use special powder for metal fires or a Class D extinguisher, and do not use water (Angstrom, Prochem and SAM SDS).
  why: Holmium is a lanthanide metal (Ho, atomic number 67) with the highest magnetic moment of any naturally occurring element, 10.6 μB. That property makes it the metal of choice for the pole pieces of the strongest static magnets. It also absorbs neutrons strongly, so it is used as a burnable poison in some reactors. The metal is soft and silvery and forms a yellowish oxide in air. The sources read give no flight record for holmium metal. Its space-relevant presence is limited to laboratory and ground materials, so no space-application claim is made for it here.
  uses:
    - where: Reactor burnable poison
      line: Wikipedia says holmium is used as a burnable poison to regulate nuclear reactors, because it absorbs neutrons strongly.
    - where: Strong static magnets
      line: Wikipedia says holmium has the highest magnetic permeability and magnetic saturation of any element and is used for the pole pieces of the strongest static magnets.
    - where: Optical calibration standards
      line: Wikipedia says holmium oxide glass and solutions have sharp absorption peaks from 200 to 900 nm and are used to calibrate spectrophotometers. This is the oxide, not the metal.
  can_do:
    - label: Carry a large magnetic moment
      value: 10.6 μB
      line: Holmium has the highest magnetic moment of any naturally occurring element, 10.6 μB per atom (Wikipedia).
    - label: Absorb neutrons
      value: about 64 barns
      line: The Goodfellow page gives a neutron absorption cross-section of about 64 barns. No isotope or temperature is stated.
    - label: Weight
      value: 8.795 g/cm3
      benchmark: density
      line: Density is 8.795 g/cm3 at 20 °C in the Wikipedia infobox, and WebElements prints 8795 kg/m3.
    - label: Melting
      value: 1474 °C
      benchmark: melting_point
      line: Melting point is 1474 °C in the Goodfellow page and the Angstrom and Prochem SDS sheets. Wikipedia gives 1461 °C.
    - label: Stiffness
      value: 64.8 GPa
      benchmark: elastic_modulus
      line: Young's modulus is 64.8 GPa in the Wikipedia infobox, and WebElements prints 65 GPa.
    - label: Heat conduction
      value: 16.2 W/(m·K)
      benchmark: thermal_conductivity
      line: Thermal conductivity is 16.2 W/(m·K) in the Wikipedia infobox, and WebElements prints 16 W/(m·K).
  compare: Holmium is a dense rare-earth metal, at 8.795 g/cm3, with a melting point of 1461 to 1474 °C depending on the source. Its thermal conductivity of 16.2 W/(m·K) is modest for a metal. Its magnetic moment is the property that matters most for its uses. It tarnishes in moist air and reacts with water, so it needs dry handling. No comparison profile is carried in this file, so the rows below list holmium values only.
  compare_rows:
    - label: Density
      benchmark: density
    - label: Melting point
      benchmark: melting_point
    - label: Thermal conductivity
      benchmark: thermal_conductivity
  recipe:
    line: Holmium is a single-element metal (Ho). Wikipedia says it is commercially extracted from monazite sand by ion exchange, and it is isolated by reducing its anhydrous chloride or fluoride with metallic calcium. It is a lanthanide and forms mainly the +3 oxidation state.
    parts:
      - name: Holmium
        symbol: Ho
        atoms: 1
        atomic_weight: 164.93033
        role: The whole material. The Goodfellow page does not state a purity, and the SDS sheets list the powder as 100 % holmium (CAS 7440-60-0).
  handling:
    - Keep the metal dry and sealed under inert gas, and avoid moisture (Angstrom and Prochem SDS).
    - Store in a cool, dry, well-ventilated place away from water, oxidizers and acid chlorides (Prochem SDS).
    - Do not use water on a fire. Use special powder for metal fires or a Class D extinguisher (Angstrom, Prochem, SAM SDS).
    - Use local exhaust and an approved respirator when dust is generated (Prochem SDS).
  good_for:
    - 'Magnetic pole pieces: holmium has a magnetic moment of 10.6 μB, the highest of any naturally occurring element (Wikipedia).'
    - 'Neutron absorption: holmium is used as a burnable poison in nuclear reactors (Wikipedia, Goodfellow).'
    - 'Optical calibration: holmium oxide solutions and glasses are used as calibration standards for spectrophotometers (Wikipedia).'
  watch_out:
    - Powder and fines are flammable solids (H228) and can ignite, and contact with water releases a flammable gas (H260) (Angstrom and Prochem SDS).
    - Holmium tarnishes and then oxidizes quickly in moist air and at higher temperatures (Wikipedia).
    - 'Supply is concentrated: China produced about 69 % of world rare-earth mine output in 2025, and China added holmium to its export controls in October 2025 (USGS). That expansion was suspended for one year in November.'
    - The sources disagree on melting point, boiling point and the packing group, and most physical values come from one encyclopedia or one data page.
  verdict: Holmium has the highest magnetic moment of any naturally occurring element, and it is also a strong neutron absorber. The metal is used for magnetic pole pieces and reactor poisons, and the oxide is used as an optical reference. The powder needs dry, inert handling because it is a flammable solid and reacts with water.