It's a labradorite, and a good one. I normally hate these stones, since they rarely shine more than a tiny bit, and only at one angle, and in certain types of light and then you might get a flash of yellow or blue-gray.
But this had an amazing blue that changes shade at different angles and is visible even indoors under fluorescent office lights. Kewl.
Love this one. Love it. Wear it everywhere. Bad guys totally avoid me now.