amethyst

nouns

a transparent purple variety of quartz; used as a gemstone
is a type of (narrower)
a hard glossy mineral consisting of silicon dioxide in crystal form; present in most rocks (especially sandstone and granite); yellow sand is quartz with iron oxide impurities
is a type of (narrower)
a gemstone having the property of transmitting light without serious diffusion

adjectives

of a moderate purple color
is similar to
being or having or characterized by hue