Boy, I liked this one a lot. First of all, I love the geologic nature of it all. Mr. Newton, you had me at "garnet." When I was in grade school I attended a day camp called "Nature Training School," and one of the activities we had was "Rocks & Minerals." We were given hammers, chisels, and goggles, and let loose on a rock ledge. Ha! Can you imagine that happening today? Anyway, it was mostly schist and quartz or feldspar, but occasionally you'd get a hunk of tourmaline, and if you were really lucky, a little chip of garnet.
Where was I? Oh, right, the puzzle. So anyway, you've got the circled minerals, or semi-precious stones, and instead of having them in a jewelry setting, you've got the word "SET" running through them! Multi-faceted indeed! And, of course, there's the fact that gemstones are, themselves faceted.
There's a ton of theme material - seven answers containing "SET" running through seven answers containing minerals, plus the two-answer revealer - all symmetrical! - and hardly any of it is tortured. I mean, GAMETHESYSTEM (67A: Exploit a loophole, say) is perfectly fine, and he found an "amethyst" in there! And POPAWHEELIE (85A: Lean back and enjoy the ride?) is great by itself, and pulling "opal" out is just a bonus.
The fill was very good, too. Some Huygens entries (SEXIER, DCUP, NYMPHOS), some fancy language stuff (111A: Company with two lameds in its name (ELAL)), and some fun stuff (18A: Bad recollection? (REPO)).
Favorite clue: 45A: You may put stock in it (SOUP).
Very enjoyable Sunday!