n. 月长石

[ noun ]
a transparent or translucent gemstone with a pearly luster; some specimens are orthoclase feldspar and others are plagioclase feldspar
<noun.substance>

Moonstone \Moon"stone`\ (m[=oo]n"st[=o]n`), n. (Min.)
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.