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Brooch with rhodium plate
MFA# 2006.261


A white, naturally occurring metallic element. Rhodium was discovered by William Wollaston in 1803. It is a very rare element belonging to the platinum group. Rhodium has an estimated concentration of 0.01 ppm in the earth's crust. It is extracted from platinum ores such as rhodite, sperrylite, and iridosmine. Metallic rhodium is used as an alloy with Platinum. It is used as a nontarnishing plating finish for silverware and jewelry. Rhodium is also used for high-reflectivity mirror-surfaces on searchlights, optical instruments, and cinema projectors.

Synonyms and Related Terms

Rh; rodio (It., Esp.); Ródio (Port.)


  • Powder is flammable.
  • Echemi: SDS

Physical and Chemical Properties

Soluble in fused potassium bisulfate. Insoluble in acids and aqua regia.

Face-centered cubic crystal.

Composition Rh (atomic no. 45)
CAS 7440-16-6
Mohs Hardness 6.0
Melting Point 1966 C
Density 12.41 g/ml
Molecular Weight atomic wt = 102.91
Boiling Point 3600-3825 C

Resources and Citations

  • G.S.Brady, Materials Handbook, McGraw-Hill Book Co., New York, 1971 Comment: p.668
  • Richard S. Lewis, Hawley's Condensed Chemical Dictionary, Van Nostrand Reinhold, New York, 10th ed., 1993
  • Van Nostrand's Scientific Encyclopedia, Douglas M. Considine (ed.), Van Nostrand Reinhold, New York, 1976
  • Random House, Webster's Encyclopedic Unabridged Dictionary of the English Language, Grammercy Book, New York, 1997
  • The Merck Index, Martha Windholz (ed.), Merck Research Labs, Rahway NJ, 10th edition, 1983 Comment: entry 8353
  • The American Heritage Dictionary or Encarta, via Microsoft Bookshelf 98, Microsoft Corp., 1998
  • Chemical & Engineering News, American Chemical Society, Washington DC, 81 (36) , Sept. 8, 2003 Comment: Jack Halpern, p. 114: discovered in 1803 by English chemist William H. Wollaston