lanthanum

American  

[lan-thuh-nuhm] / ˈlæn θə nəm /

noun

Chemistry.

1. a rare-earth, trivalent, metallic element, allied to aluminum, found in certain minerals, as monazite. La; 138.91; 57; 6.15 at 20°C.

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lanthanum British  

/ ˈlænθənəm /

noun

1. a silvery-white ductile metallic element of the lanthanide series, occurring principally in bastnaesite and monazite: used in pyrophoric alloys, electronic devices, and in glass manufacture. Symbol: La; atomic no: 57; atomic wt: 138.9055; valency: 3; relative density: 6.145; melting pt: 918°C; boiling pt: 3464°C

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lanthanum Scientific  

/ lăn′thə-nəm /

1. A soft, malleable, silvery-white metallic element of the lanthanide series. It is used to make glass for lenses and lights for movie and television studios. Atomic number 57; atomic weight 138.91; melting point 920°C; boiling point 3,469°C; specific gravity 5.98 to 6.186; valence 3.

2. See Periodic Table

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Etymology

Origin of lanthanum

< New Latin (1841), equivalent to lanthan- (< Greek lanthánein to escape notice; referring to its position on the periodic table) + -um, variant of -ium -ium

Example Sentences

The ore from MP’s External link Mountain Pass mine contains a lot of cerium, lanthanum, neodymium, praseodymium, and samarium.

From Barron's • Nov. 13, 2025

"The objective of the liquid separation unit will be to purify cerium on one side, lanthanum on the other side," explains production manager Florian Gouneau as we walk up a flight of metal stairs.

From BBC • Aug. 6, 2025

But, at room temperature, the number of hydrogens attached to lanthanum fluctuates between 2 and 3, making it impossible to have efficient conduction.

From Science Daily • Dec. 22, 2023

Loeb says traces of three rare elements — beryllium, lanthanum and uranium — suggest the spheres come from outside of our solar system.

From Salon • Sep. 1, 2023

Who, then, will be the first to discover a use for indium, germanium, terbium, thulium, lanthanum, neodymium, scandium, samarium and others as unknown to us as tungsten was to our fathers?

From Creative Chemistry Descriptive of Recent Achievements in the Chemical Industries by Slosson, Edwin E.