Source : Webster's Revised Unabridged Dictionary (1913)

Pollucite \Pol"lu*cite\, n. [See {Pollux}, and 4th {Castor}.]
   (Min.)
   A colorless transparent mineral, resembling quartz, occurring
   with castor or castorite on the island of Elba. It is a
   silicate of alumina and c[ae]sia. Called also {pollux}.

Source : WordNet®

pollucite
     n : a rare mineral that is an important source of cesium