Among the rare earth elements erbium is considered one of the air stable metals. Strictly speaking, this is not true however. While it does remain lustrous indefinitely, after long exposure to air pieces of the metal begin gathering a fine dust that flakes off and coats the base where it’s stored. The effect is slight and since it does not stick it’s easy to not notice.

Erbium does not have any remarkable properties to stand out among the other rare earths. It is used for tinting glass, specialty lasers and as a doping agent in phosphorescent materials to yield precise colors. None of these spell the need for large amounts of the material so its price has remained relatively modest.

At least with these little chunks in argon your sample of erbium will be spared any corrosion at all.