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A soft, silvery-white metallic rare-earth element. Lanthanum is a malleable metal that occurs naturally in the minerals monazite and bastnasite. First identified by Mosander in 1839, it ranks 57th in abundance of elements in the earth's crust. Lanthanum oxidizes in air with the corroded layers spalling off to expose new surfaces. The trivalent element is very reactive and forms alloys and salts readily. Lanthanum is used in electronic devices, and for rocket propellants, and x-ray screen phosphors.

Synonyms and Related Terms



  • Spontaneous ignition of powder.
  • Ingestion may cause liver damage and delay blood clotting.

Physical and Chemical Properties

Soluble in acids. Slowly decomposes in water to form lanthanum hydroxide and hydrogen.

Composition La (atomic no. 57)
CAS 7439-91-0
Melting Point 920 C
Density 6.19 g/ml
Molecular Weight at. wt. = 138.9055
Boiling Point 3464 C

Resources and Citations

  • 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
  • The Merck Index, Martha Windholz (ed.), Merck Research Labs, Rahway NJ, 10th edition, 1983 Comment: entry 5374

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