noun.
A metamorphic rock composed chiefly of amphibole and plagioclase feldspar and having little or no quartz.
The Century Dictionary and Cyclopedia
noun.
A rock belonging to the class of the crystalline schists, and consisting largely of green hornblende, together with quartz or feldspar, or both. It is always more or less distinctly in beds like gneiss.
the GNU version of the Collaborative International Dictionary of English
noun.
a metamorphic rock composed chiefly of amphibole and plagioclase.