the GNU version of the Collaborative International Dictionary of English
adj. Somewhat precious. Used mostly of gemstones used in jewelry, such as amethyst, garnet, or iolite, which are sufficiently rare to have commercial value, but are not considered as precious, as are the diamond, emerald, and ruby.
The Century Dictionary and Cyclopedia
Valuable, but less so than the most highly prized objects of similar nature.
WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
adj. used of gemstones having less commercial value than precious stones
Word Usage
"We don't bother much with what Kimmer terms semiprecious, though he has some fine turquoise he says extremely valuable."