Random gemstone of the day: Ammolite.
What you're looking at here is more or less fossilized mother-of-pearl from ammonites. I'm oversimplifying, but you get the idea. Fossilized shell.
Ammolite is Alberta's provincial gemstone. Most of the world's ammolite comes from quarries near Lethbridge, Alberta. Prized for its colour shifting qualities, ammolite itself is thin and fragile, so for jewellery it is always mounted as a doublet (ammolite glued to a stronger backing stone) or triplet (clear stone in front, ammolite in the centre, and a backing stone).
The free-form stone at the top of the photo is considered lower quality because it only has a red to green shift, but that's the only way I could have afforded that size of a piece. With ammolite, more colours usually equals more expensive, but I kind of like this example's Christmasy vibe. The lower stone was a gift, and is a mid-range stone mounted as a triplet with faceted quartz. It adds yellow to the mix, but it doesn't have much of the blue that would make it more costly.
For me, that means I actually wear it instead of just worrying that it will get damaged...
Anyway, the reason that you're seeing ammolite today is that it also counts as a Fossil Friday. Always multipurpose your pointless photos, folks. 😉