a white soft metallic element that tarnishes readily; occurs in rare earth minerals and is usually classified as a rare earth
A chemical element (symbol La) with an atomic number of 57: a soft, ductile, silvery-white metal that tarnishes slowly when exposed to air.
The name lanthanum comes from the Ancient Greek word lanthánō, meaning "to escape notice." This refers to the fact that the element remained undetected within mineral ores for a long time.