Tanzanite is the singular one. It comes from a few square kilometres at the foot of Kilimanjaro and nowhere else on earth — not marketing, just geology. Whatever conditions made it happened once.
This oval is domed rather than faceted, which is unusual for the material; tanzanite is nearly always cut for sparkle. As a cabochon you trade fireworks for color, and what you get is a deep, uninterrupted violet-blue that shifts toward blue in daylight and toward purple under a lamp.
I bezel-set it plainly so nothing shades the stone and both colors stay available to you.
It wears rich and quietly serious — a stone with a finite supply and a very specific glow.
