adularescence

No, "adularescence" isn't the stage between adolescence and adulthood; it's "[w]hen a gem displays a billowy floating light which appears to come from below the surface," according to the Optical Phenomena in Gemstones page. (Which is a pretty darn nifty page, full of cool info and images.)

That page also says that the term comes from a name for moonstone: "adularia." Apparently a synonym is "shiller."

The page also introduced me to the words "rutile" and "serefinites" (both types of stones), "labradorescence" (the kind of iridescence foundin Labradorite), "drusy" (an adjective meaning "covered with tiny crystals"), and "aventurescence" (the "spangly glow" of (for example) bits of mica embedded in other minerals).