I'm NOT a geologist or the like and I ain't gonna lie...
Never heard that before.
Internet search turned up with that question asked on different sites but went unanswered there too.
My Best Guess?
A violet-to-maroon stone, lightweight and of slight transparency who's Metaphysical Purpose include finding a woman named Donna...and asking if she's drunk.
My apologies, I couldn't help myself :)
Good luck in your search!
~ Kat ~