spore: profile
id: rubidium
spore_version: 0.2
family: alkali-metals
name: Rubidium
abbreviation: Rb
role: atomic clock reference metal
category: metals
type: heavy-metals
summary: Rubidium (Rb, CAS 7440-17-7) is a soft, silvery alkali metal with atomic number 37. An Alfa Aesar safety data sheet gives its density as 1.532 g/cm3 at 20 °C, and sources in this profile give its melting point as 38.9 °C, 39.31 °C and 39.5 °C. It reacts violently with water and tarnishes in air, so it is stored under dry inert gas. The USGS found no reported rubidium mine production worldwide in 2025, and its main use named in the source is as an atomic resonance-frequency reference, which is the basis of rubidium clocks flown on navigation satellites.
best_for: 'Atomic frequency references: rubidium clocks were flown on GPS Block IIR satellites and on the Galileo test satellite GIOVE-A (NASA-hosted paper; Airbus catalogue)'
weakest_at: 'Handling: it reacts violently with water and tarnishes in air, and CAMEO Chemicals says it burns spontaneously in dry oxygen'
identity:
  formula: Rb
  cas: 7440-17-7
  source: pubchem-rb
  where: PubChem compound record CID 5357696, section 2.3.1 (CAS)
tags:
  environments: []
  stresses: []
  applications:
    - electronics-and-chips
    - optics-and-cameras
properties:
  - benchmark: density
    label: Density at 20 °C, Alfa Aesar safety data sheet
    value: 1.532
    unit: g/cm3
    scope: material
    conditions:
      form: solid metal, product 10315 (rubidium metal, 7440-17-7)
      temperature: 20 °C
      unit_in_source: g/cm³
    method: Value printed in a supplier safety data sheet
    status: ground
    source: purdue-rb-sds
    where: Section 9, Density at 20 °C (68 °F)
  - benchmark: density
    label: Density, element (Wolfram ElementData)
    value: 1.532
    unit: g/cm3
    scope: material
    conditions:
      form: solid metal
      temperature: not stated on the page
    method: Value printed on a reference data page that cites Mathematica ElementData
    status: ground
    note: Agrees with the safety data sheet value above.
    source: periodictable-rb
    where: Overview and Bulk physical properties, Density
  - benchmark: density
    label: Density of solid (WebElements)
    value: 1532
    unit: kg/m3
    scope: material
    conditions:
      form: solid metal
      temperature: not stated on the page
      unit_in_source: kg m‑3
    method: Value printed on a reference data page
    status: ground
    note: The same figure as 1.532 g/cm3 in other sources, in SI units.
    source: webelements-rb
    where: Density properties, Density of solid
  - benchmark: density
    label: Density of liquid rubidium (Wolfram ElementData)
    value: 1.46
    unit: g/cm3
    scope: material
    conditions:
      form: liquid metal
      temperature: not stated on the page
    method: Value printed on a reference data page
    status: ground
    source: periodictable-rb
    where: Bulk physical properties, Density (Liquid)
  - benchmark: melting_point
    label: Melting point, Alfa Aesar safety data sheet
    value: 38.9
    unit: °C
    scope: material
    conditions:
      form: rubidium metal
      unit_in_source: 38.9 °C (102 °F)
      pressure: not stated
    method: Value printed in a supplier safety data sheet
    status: ground
    note: Three sources give 38.9 °C, 39.31 °C and 39.5 °C. This profile keeps all three rather than choosing one.
    source: purdue-rb-sds
    where: Section 9, Melting point/Melting range
  - benchmark: melting_point
    label: Melting point, Wolfram ElementData
    value: 39.31
    unit: °C
    scope: material
    conditions:
      form: rubidium metal
      pressure: not stated
    method: Value printed on a reference data page that cites Mathematica ElementData
    status: ground
    note: See the safety data sheet value of 38.9 °C; the sources disagree by about one kelvin.
    source: periodictable-rb
    where: Overview and Thermal properties, Melting Point
  - benchmark: melting_point
    label: Melting point, PAC Chemical Database (via PubChem)
    value: 39.5
    unit: °C
    scope: material
    conditions:
      form: rubidium
      pressure: not stated
    method: Value listed in the PubChem record, attributed to the U.S. DOE PAC Chemical Database
    status: ground
    source: pubchem-rb
    where: Section 3.2.3 Melting Point
  - benchmark: boiling_point
    label: Boiling point, Wolfram ElementData
    value: 688
    unit: °C
    scope: material
    conditions:
      pressure: not stated on the page
    method: Value printed on a reference data page that cites Mathematica ElementData
    status: ground
    source: periodictable-rb
    where: Overview and Thermal properties, Boiling Point
  - benchmark: specific_heat
    label: Specific heat capacity, solid phase
    value: 364
    unit: J/(kg K)
    scope: material
    conditions:
      phase: solid
      temperature: not stated on the page
    method: Value printed on a reference data page; the page notes it is given for the solid phase
    status: ground
    source: periodictable-rb
    where: Thermal properties, Specific Heat
  - benchmark: thermal_conductivity
    label: Thermal conductivity
    value: 58
    unit: W/(m K)
    scope: material
    conditions:
      temperature: not stated on the page
    method: Value printed on a reference data page
    status: ground
    note: WebElements prints the same 58 W m-1 K-1.
    source: periodictable-rb
    where: Thermal properties, Thermal Conductivity
  - benchmark: elastic_modulus
    label: Young's modulus
    value: 2.4
    unit: GPa
    scope: material
    conditions:
      temperature: not stated on the page
    method: Value printed on a reference data page
    status: ground
    note: Wolfram ElementData prints the same 2.4 GPa.
    source: webelements-rb
    where: Elastic properties, Young's modulus
  - benchmark: bulk_modulus
    label: Bulk modulus
    value: 2.5
    unit: GPa
    scope: material
    conditions:
      temperature: not stated on the page
    method: Value printed on a reference data page
    status: ground
    source: periodictable-rb
    where: Bulk physical properties, Bulk Modulus
  - benchmark: molar_mass
    label: Molecular weight of the element (PubChem computed)
    value: 85.468
    unit: g/mol
    scope: material
    conditions:
      form: Rb, element, computed from the isotope mix
    method: Computed value printed by PubChem 2.2 (release 2025.05.06)
    status: calculated
    source: pubchem-rb
    where: Section 3.1 Computed Properties, Molecular Weight
  - benchmark: isotopic_abundance
    label: Mole fraction of rubidium-85 in natural rubidium
    value: 0.7217
    unit: '-'
    scope: material
    conditions:
      isotope: 85Rb
      basis: standard isotopic composition, mole fraction; uncertainty printed as (2)
    method: Value printed on the NIST atomic weights and isotopic compositions page
    status: ground
    source: nist-rb
    where: Table of isotopes, row 85, Isotopic composition (mole fraction)
  - benchmark: isotopic_abundance
    label: Mole fraction of rubidium-87 in natural rubidium
    value: 0.2783
    unit: '-'
    scope: material
    conditions:
      isotope: 87Rb
      basis: standard isotopic composition, mole fraction; uncertainty printed as (2)
    method: Value printed on the NIST atomic weights and isotopic compositions page
    status: ground
    source: nist-rb
    where: Table of isotopes, row 87, Isotopic composition (mole fraction)
  - benchmark: atomic_number
    label: Atomic number
    value: 37
    unit: '-'
    scope: material
    conditions:
      element: rubidium, Rb
    method: Value printed on a reference data page
    status: ground
    source: periodictable-rb
    where: Overview, Atomic Number
  - benchmark: first_ionization_energy
    label: First ionization energy
    value: 403
    unit: kJ/mol
    scope: material
    conditions:
      basis: first value of the ionization energy list printed on the page
    method: Value printed on a reference data page
    status: ground
    source: periodictable-rb
    where: Reactivity, Ionization Energies (first entry of the list)
  - benchmark: electronegativity
    label: Electronegativity
    value: 0.82
    unit: '-'
    scope: material
    conditions:
      scale: scale not named on the page
    method: Value printed on a reference data page
    status: ground
    source: periodictable-rb
    where: Reactivity, Electronegativity
  - benchmark: atomic_radius
    label: Atomic radius
    value: 265
    unit: pm
    scope: material
    conditions:
      basis: as printed on the page; definition not stated
    method: Value printed on a reference data page
    status: ground
    source: periodictable-rb
    where: Atomic dimensions and structure, Atomic Radius
  - benchmark: lattice_constant
    label: Lattice constant of the rubidium cell as printed
    value: 558.5
    unit: pm
    scope: material
    conditions:
      structure: three equal constants with right angles printed; space group number 229 printed on the same page
      temperature: not stated on the page
    method: Value printed on a reference data page
    status: ground
    note: PubChem lists a different cell for rubidium (from an older paper); the two are not reconciled here.
    source: periodictable-rb
    where: Atomic dimensions and structure, Lattice Constants
  - benchmark: crustal_abundance
    label: Abundance in Earth's crust as printed
    value: 0.006
    unit: '%'
    scope: material
    conditions:
      basis: percent in Earth's crust, as printed on the page
    method: Value printed on a reference data page
    status: ground
    source: periodictable-rb
    where: Abundances, % in Earth's Crust
  - benchmark: recoverable_reserves
    label: World recoverable reserves of rubidium materials (USGS estimate)
    value: 200000
    bound: upper
    unit: tons
    scope: material
    conditions:
      basis: recoverable rubidium materials; USGS names Australia, Canada, China and Namibia as the countries estimated to hold them
      note: printed as less than the figure
    method: Estimate printed in the USGS Mineral Commodity Summaries chapter
    status: ground
    source: usgs-mcs2026-rubidium
    where: World Mine Production and Reserves
corrosion:
  - environment: Air at room temperature
    headline: Rubidium tarnishes rapidly in air; no corrosion rate was found in any source opened.
    effect: CAMEO Chemicals says rubidium tarnishes rapidly upon exposure to air, and PubChem's summary of the same source says it tarnishes in air. Neither gives a rate, a film thickness or a time scale, so none is recorded. The supplier safety data sheet asks for storage under dry inert gas and away from air.
    rating: unknown
    conditions:
      exposure: room-temperature air; humidity, time and temperature not stated
    source: cameo-rb
    where: Air and Water Reactions (section 9.7.1)
  - environment: Liquid water and moist air
    headline: 'Water is the severe case: the reaction gives corrosive rubidium hydroxide and flammable hydrogen.'
    effect: CAMEO Chemicals says rubidium reacts violently with water to form corrosive rubidium hydroxide and hydrogen, a flammable gas, and that the heat of the reaction usually ignites the hydrogen. The safety data sheet also lists a severe skin burn and eye damage hazard (H314).
    rating: severe
    conditions:
      exposure: contact with liquid water or moisture
    source: cameo-rb
    where: Air and Water Reactions (section 9.7.1); Reactivity Alerts (section 9.7.3)
risks:
  hazards:
    - text: PubChem's GHS summary for rubidium lists H260 (in contact with water releases flammable gases which may ignite spontaneously) and H314 (causes severe skin burns and eye damage), with signal word Danger.
      ghs:
        - H260
        - H314
      source: pubchem-rb
      where: Section 9.1.1 GHS Classification
    - text: The Alfa Aesar safety data sheet (copy hosted by Purdue) gives the same two hazard statements, Danger, and the precautionary statement P231+P232, which reads 'Handle under inert gas. Protect from moisture.'
      ghs:
        - H260
        - H314
      source: purdue-rb-sds
      where: Section 2, GHS label elements
    - text: For fires involving rubidium, the Emergency Response Guidebook guide quoted by CAMEO Chemicals says do not use water or foam, and suggests dry chemical, dry sand or class D extinguishers for metal fires.
      ghs: []
      source: cameo-rb
      where: Fire Fighting and Emergency Response Planning (ERG Guide 138)
    - text: The Emergency Response Guidebook first-aid text says to wipe the metal off the skin at once and flush skin or eyes with running water.
      ghs: []
      source: cameo-rb
      where: First Aid, Specific First Aid (ERG Guide 138)
  failure_risks:
    - mode: Reaction with water or moist air
      trigger: Water or humid air reaching the metal
      consequence: Flammable hydrogen gas, usually ignited by the heat of the reaction, plus corrosive rubidium hydroxide (CAMEO Chemicals).
      severity: high
      source: cameo-rb
      where: Air and Water Reactions (section 9.7.1)
    - mode: Spontaneous burning in dry oxygen
      trigger: Exposure to dry oxygen; readily catches fire in air when molten
      consequence: The metal burns spontaneously in dry oxygen, according to the CAMEO Chemicals reactivity profile reproduced in PubChem.
      severity: high
      source: pubchem-rb
      where: Section 9.7.4, Reactivity Profile
    - mode: Tarnish in air
      trigger: Exposure to air
      consequence: A tarnish film forms on the metal; no thickness or rate is recorded in the sources opened.
      severity: low
      source: cameo-rb
      where: Air and Water Reactions (section 9.7.1)
  side_effects:
    - text: Hydrogen and corrosive rubidium hydroxide are released when the metal reacts with water, and the hydrogen is flammable.
      affects: Storage area and the people handling the metal
      source: cameo-rb
      where: Air and Water Reactions (section 9.7.1)
  handling:
    - text: Handle under dry protective gas, keep the container tightly sealed, and store under dry inert gas, away from water, moisture, air and oxidizing agents, according to the Alfa Aesar safety data sheet.
      source: purdue-rb-sds
      where: Section 7, Handling and storage
    - text: For a spill, cover with dry earth, dry sand or another non-combustible material and do not apply water, per the Emergency Response Guidebook guide quoted by CAMEO Chemicals.
      source: cameo-rb
      where: Nonfire Spill Response (section 9.5.1)
  mitigations:
    - text: Use dry chemical, dry sand, sodium chloride powder, graphite powder or class D extinguishers on metal fires (Emergency Response Guidebook guide quoted by CAMEO Chemicals).
      source: cameo-rb
      where: Emergency Response Planning, Fire Involving Metals or Powders
uses:
  - application: electronics-and-chips
    device: Rubidium atomic frequency standard on navigation satellites
    example: Airbus's catalogue entry says the Rubidium Atomic Frequency Standard was first flown on GIOVE-A, the Galileo test satellite, and has operated successfully since.
    source: satcatalog-rafs
    where: Overview of the component page
  - application: electronics-and-chips
    device: GPS Block IIR navigation satellites
    example: A NASA-hosted paper by Riley describes rubidium atomic frequency standards provided for the GPS Block IIR NAVSTAR satellites, which were to replenish and upgrade the space segment of the Global Positioning System.
    source: ntrs-riley-1990
    where: Abstract
  - application: optics-and-cameras
    device: Photomultiplier tubes, night-vision devices and photoelectric cells
    example: The USGS says rubidium's photoemissive properties make it useful for photomultiplier tubes, night-vision devices, photoelectric cells and spectrometers.
    source: usgs-mcs2026-rubidium
    where: Domestic Production and Use
supply:
  - subject: Rubidium
    abundance: Rubidium is not a major constituent of any mineral; the crustal abundance printed on the reference data page is in the properties list.
    producers: []
    critical_lists: []
    recycling: 'USGS: Recycling: None.'
    substitutes:
      - 'USGS: rubidium and cesium can be used interchangeably in many applications because they have similar physical properties and atomic radii; cesium is more electropositive and is preferred for some applications.'
    source: usgs-mcs2026-rubidium
    where: Domestic Production and Use; World Mine Production and Reserves (the USGS prints that there were no official sources for rubidium production data in 2025, so no country shares are recorded); Recycling; Substitutes (Mineral Commodity Summaries, February 2026). Rubidium is a byproduct of pollucite (cesium) and lepidolite (lithium) mining, per the same chapter.
documents:
  - title: Alfa Aesar safety data sheet, rubidium metal, product 10315 (copy hosted by Purdue University; last revision 2015)
    type: sds
    url: https://www.physics.purdue.edu/primelab/safety/MSDS/SDS/rubidium%20metal%20%20-%20Alfa%2010315.pdf
    year: 2015
  - title: 'PubChem: Rubidium, CID 5357696, GHS and computed properties'
    type: database
    url: https://pubchem.ncbi.nlm.nih.gov/compound/Rubidium
    year: 2026
  - title: 'CAMEO Chemicals: Rubidium (NOAA chemical 1439)'
    type: database
    url: https://cameochemicals.noaa.gov/chemical/1439
    year: 2026
  - title: 'USGS Mineral Commodity Summaries 2026: Rubidium'
    type: report
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-rubidium.pdf
    year: 2026
  - title: 'NIST: Atomic weights and isotopic compositions for rubidium'
    type: database
    url: https://physics.nist.gov/cgi-bin/Compositions/stand_alone.pl?ele=Rb&all=all&ascii=html
    year: 2026
  - title: 'WebElements: Rubidium physical properties'
    type: database
    url: https://www.webelements.com/rubidium/physics.html
    year: 2026
  - title: 'Wolfram ElementData: Rubidium (periodictable.com)'
    type: database
    url: https://periodictable.com/Elements/037/data.html
    year: 2026
  - title: Airbus Rubidium Atomic Frequency Standard component entry (satcatalog.com)
    type: database
    url: https://www.satcatalog.com/component/rubidium-atomic-frequency-standard/
    year: 2026
  - title: Rubidium atomic frequency standards for GPS Block IIR (NASA NTRS 19910016457)
    type: report
    url: https://ntrs.nasa.gov/citations/19910016457
    year: 1990
gaps:
  - No flight, radiation, vacuum, outgassing or thermal-cycling result for rubidium metal was found in any source opened. The satellite-clock sources describe units, not the metal.
  - Melting point is recorded from three sources that disagree (38.9, 39.31 and 39.5 °C); none is chosen as the reference value.
  - Electrical resistivity and conductivity are printed with exponents on both data pages and were not recorded (exponent-form values).
  - Mechanical strength of pure rubidium (yield, tensile, hardness in engineering units) was not found; the Mohs and Brinell figures on the reference page are not recorded because no canonical property name fits.
  - PubChem lists a different crystal cell for rubidium from an older paper; the cubic cell in the properties is from Wolfram ElementData only, and the conflict is not resolved.
  - The manufacturing process for rubidium metal was not described in any source opened, so the recipe gives composition only.
  - No corrosion rate, film thickness or ageing time for rubidium in air or under inert gas was found; the corrosion rating for air is unknown.
  - 'No country shares of production are recorded: the USGS states that there were no official sources for rubidium production data in 2025.'
  - The USGS chapter text read does not state whether rubidium is on a critical-minerals list, so critical_lists is empty.
  - DTIC clock papers on the space rubidium clock for Galileo and on GPS rubidium clock life tests could not be opened (the pages returned a maintenance notice), so their design figures are not recorded.
  - 'Several property names are not in spores/property-canon.yaml and were used as snake_case names: molar_mass, isotopic_abundance, atomic_number, first_ionization_energy, electronegativity, atomic_radius, lattice_constant, crustal_abundance and recoverable_reserves.'
  - No designations (UNS, EN, DIN, JIS) apply to the element; the CAS number is the identifier used.
sources:
  purdue-rb-sds:
    title: 'Safety data sheet: Rubidium metal, Alfa Aesar product 10315 (copy hosted by Purdue University)'
    id: Alfa Aesar product 10315, CAS 7440-17-7
    url: https://www.physics.purdue.edu/primelab/safety/MSDS/SDS/rubidium%20metal%20%20-%20Alfa%2010315.pdf
    year: 2015
    kind: datasheet
    license: Supplier safety data sheet (cited, not reproduced)
  pubchem-rb:
    title: 'PubChem compound record: Rubidium (CID 5357696)'
    id: PubChem CID 5357696; CAS 7440-17-7
    url: https://pubchem.ncbi.nlm.nih.gov/compound/Rubidium
    year: 2026
    kind: database
    license: Public database record (cited)
  cameo-rb:
    title: 'CAMEO Chemicals: Rubidium (NOAA chemical 1439), with Emergency Response Guidebook guide 138'
    id: UN 1423 (as printed on the record)
    url: https://cameochemicals.noaa.gov/chemical/1439
    year: 2026
    kind: database
    license: NOAA public record (cited)
  usgs-mcs2026-rubidium:
    title: 'Mineral Commodity Summaries 2026: Rubidium (U.S. Geological Survey, February 2026)'
    id: USGS Mineral Commodity Summaries, February 2026
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-rubidium.pdf
    year: 2026
    kind: report
    license: U.S. government work (cited)
  nist-rb:
    title: 'NIST: Atomic weights and isotopic compositions, rubidium (Rb, atomic number 37)'
    id: NIST Physical Measurement Laboratory
    url: https://physics.nist.gov/cgi-bin/Compositions/stand_alone.pl?ele=Rb&all=all&ascii=html
    year: 2026
    kind: database
    license: U.S. government work (cited)
  webelements-rb:
    title: 'WebElements: Rubidium, physical properties'
    id: WebElements periodic table, element 37
    url: https://www.webelements.com/rubidium/physics.html
    year: 2026
    kind: database
    license: Cited, not reproduced
  periodictable-rb:
    title: 'Wolfram ElementData: Technical data for Rubidium (periodictable.com)'
    id: Mathematica ElementData, Wolfram Research
    url: https://periodictable.com/Elements/037/data.html
    year: 2026
    kind: database
    license: Cited, not reproduced
  satcatalog-rafs:
    title: Rubidium Atomic Frequency Standard (Airbus), component entry, satcatalog.com
    id: Airbus Rubidium Atomic Frequency Standard
    url: https://www.satcatalog.com/component/rubidium-atomic-frequency-standard/
    year: 2026
    kind: database
    license: Cited, not reproduced
  ntrs-riley-1990:
    title: Rubidium atomic frequency standards for GPS Block IIR (Riley, Edgerton, Germeshausen and Grier)
    id: NASA NTRS citation 19910016457
    url: https://ntrs.nasa.gov/citations/19910016457
    year: 1990
    kind: paper
    license: NASA public record (cited)
license: CC-BY-4.0
updated: '2026-11-01'
review:
  status: draft
  method: assistant
  checked_values: 22
  unreachable: 2
  caveats: 3
  note: 'Read by an AI assistant on 2026-11-01 from the pages and PDFs named in each entry. verify-values found all 20 other values printed in their sources. Two PubChem values (melting point 39.5 °C and molar mass 85.468 g/mol) could not be re-checked by script because the PubChem page returns a browser-check shell to curl; they were read in a browser in this run. Caveats: the melting point disagrees across three sources and all three are kept; the PubChem page is JavaScript-rendered; the corrosion rating for air is unknown because no rate was found.'
story:
  recipe:
    line: 'Rubidium is a single element, Rb, with atomic number 37, and it is an alkali metal. Natural rubidium is a mix of two isotopes: rubidium-85 with a mole fraction of 0.7217 and rubidium-87 with 0.2783, per the NIST table. No source opened for this profile describes how the metal is made.'
    parts:
      - name: Rubidium
        symbol: Rb
        atoms: 1
        atomic_weight: 85.468
        role: The whole material. The element's mass is taken from PubChem's computed molecular weight, 85.468 g/mol.
  risk_groups:
    - title: For people
      level: 2
      verdict: Severe burns; reacts violently with water
      lead: Rubidium is classed as a skin corrosive and as a water-reactive substance, so it is handled as a hazardous material.
      points:
        - label: Skin and eyes
          line: The safety data sheet and PubChem's GHS summary both give H314, causes severe skin burns and eye damage.
        - label: Water
          line: H260 means contact with water releases flammable gases which may ignite spontaneously. CAMEO Chemicals says the heat of the reaction usually ignites the hydrogen.
        - label: First aid
          line: The first-aid text quoted from the Emergency Response Guidebook says to wipe the metal off the skin at once and flush with running water.
    - title: If it reacts
      level: 1
      verdict: Fire needs a dry agent, not water
      lead: These are reactions the sources describe; no incident record was opened.
      points:
        - label: Fire
          line: Do not use water or foam on a rubidium fire. Use dry chemical, dry sand or class D extinguishers, as the Emergency Response Guidebook guide quoted by CAMEO Chemicals says.
        - label: Burning
          line: PubChem's reactivity profile, reproduced from CAMEO Chemicals, says the metal burns spontaneously in dry oxygen and catches fire in air when molten.
    - title: Handling and storage
      level: 0
      verdict: Dry inert gas, sealed container
      lead: The supplier safety data sheet sets the storage rules.
      points:
        - label: Storage
          line: Handle under dry protective gas and keep the container tightly sealed. Store under dry inert gas, away from water, moisture, air and oxidizing agents.
        - label: Spills
          line: Cover a spill with dry earth, dry sand or another non-combustible material, and do not apply water.
  why: Rubidium is a soft, silvery alkali metal, and it is one of the reactive metals in its group. The USGS names its main use as an atomic resonance-frequency reference, the principle behind the rubidium clocks flown on navigation satellites. Specialty glass is the leading market for rubidium compounds according to the same USGS chapter, and the metal also appears in photomultiplier tubes, night-vision devices and catalysts. Rubidium is a byproduct of pollucite and lepidolite mining, not a primary product, so supply depends on those mines and on stockpiles.
  uses:
    - where: Navigation satellite clocks
      line: Airbus lists a Rubidium Atomic Frequency Standard that was first flown on GIOVE-A, the Galileo test satellite, with successful operation since then. A NASA-hosted paper by Riley describes rubidium atomic frequency standards provided for the GPS Block IIR satellites.
    - where: Optical sensors
      line: The USGS says rubidium's photoemissive properties make it useful for photomultiplier tubes, night-vision devices, photoelectric cells and spectrometers.
  can_do:
    - label: Set a time reference
      line: The USGS describes rubidium as an atomic resonance-frequency reference, the basis of the clocks flown for global positioning.
    - label: Respond to light
      line: Rubidium's photoemissive properties are used in photomultiplier tubes and night-vision devices, per the USGS.
    - label: Stand in for cesium
      line: The USGS says the two can be used interchangeably in many applications because of their similar physical properties and atomic radii.
  compare: The USGS says rubidium and cesium can be used interchangeably in many applications, because they have similar physical properties and atomic radii, and that cesium is the more electropositive of the two and is preferred for some uses. Within this profile, the density of 1.532 g/cm3 and the melting point of 38.9 °C in the safety data sheet are the figures to set against other metals in the same table, and the table rows below use this profile's own values.
  compare_rows:
    - label: Density
      benchmark: density
    - label: Melting point
      benchmark: melting_point
    - label: Thermal conductivity
      benchmark: thermal_conductivity
  handling:
    - Store under dry inert gas in a tightly sealed container, away from water and oxidizing agents.
    - Never use water on a rubidium fire or spill; cover spills with dry earth or dry sand.
    - 'Wear protection against severe skin burns: the GHS statement H314 applies.'
  good_for:
    - 'Timing: rubidium frequency standards were flown on navigation satellites, as the Airbus catalogue and the NASA-hosted paper describe.'
    - 'Specialty glass and optical devices: the USGS names specialty glass as the leading market, with photomultiplier tubes and night-vision devices.'
  watch_out:
    - Reacts violently with water, forming flammable hydrogen and corrosive rubidium hydroxide.
    - Tarnishes in air. No corrosion rate was found, so storage under inert gas is the only guidance in the sources.
    - 'Supply: the USGS reports no official rubidium production data for 2025, and rubidium comes mainly from byproducts.'
  verdict: Rubidium is a reactive alkali metal whose main documented use is as a frequency reference in navigation satellites. Its handling risk is high, and the sources in this profile give no space-environment data for the metal itself.