noun.
A variety of feldspar valued as a gem for its pearly translucence.
The Century Dictionary and Cyclopedia
noun.
A variety of feldspar which by reflected light presents a delicate pearly play of color not unlike that of the moon.
the GNU version of the Collaborative International Dictionary of English
noun.
A nearly pellucid variety of feldspar, showing pearly or opaline reflections from within. It is used as a gem. The best specimens come from Ceylon.