Source : Webster's Revised Unabridged Dictionary (1913)

Semiprecious \Sem`i*pre"cious\, a.
   Somewhat precious; as, semiprecious stones or metals.

Source : WordNet®

semiprecious
     adj : used of gemstones having less commercial value than precious
           stones; "such semiprecious stones as amethyst, garnet,
           jade, and tourmaline"