a. A name applied to many gemstones with a girasol effect, e.g.,
moonstone; specif. a translucent variety of "fire opal" with reddish
reflections in bright light and a faint bluish-white floating light
emanating from the center of the stone.
b. adj. Said of any gem variety, e.g., sapphire, chrysoberyl, that
exhibits a billowy, gleaming round or elongated area of light that
"floats" or moves about as the stone is turned or as the light source is
c. A name for glass spheres used in the manufacture of imitation pearls.
Dictionary of Mining, Mineral, and Related Terms