The Collaborative International Dictionary of English v.0.48:

Eucairite \Eu*cai"rite\, n. [Gr. ? seasonable, opportune; e'y^
   well, good + ? season.] (Min.)
   A metallic mineral, a selenide of copper and silver; -- so
   called by Berzelius on account of its being found soon after
   the discovery of the metal selenium.
   [1913 Webster]