In my hemisphere, Christmas comes when the nights are long, and bright colored lights help relieve the darkness while echoing the constantly lighted universe around us. The lights and colors of the mineral kingdom are constant too, for the most part. Some specimens offer a subtle mimicry of life, changing color in different lights or in different orientations. Some minerals twinkle, some glitter, some glimmer, some just shine. Then there are wonders like my fire opal ear stud, which uses all of those verbs at once. Geologists have a name for the way that opal plays with light: schiller. Some day I'll make a video that shows it better; for now enjoy it here.
I'm putting the finishing touches on the Holiday Geo-Quiz. Look for it here tomorrow.