Yeah, I don't get that, rocks like this are the +1 of the ones you're actually aiming for to make balance rings with...but...
1. They don't work to make balance rings?
2. Their value is probably low because not only are high level goldsmithers few and far between, they have just as much chance as you do to HQ them for themselves.
Sucks that getting an HQ actually works to your disadvantage (if you can't sell it reasonably) at level 48 goldsmithing is all I'm trying to say.
Today, on Darksday with a New Moon (2%), I decided to try synthing peridots. I was able to make one on my first try and ended up having a success rate of 2/8. Anyway, I wanted to make some amethyst as to try and make a balance ring (AH was out of amethyst). My one and only try resulted in a Spinel.
My goldsmithing level at the time was 48. This is just to show that you don't necessarily need to have very high goldsmithing skill to make these, but if you want to make one, synth on darksday and new moon as the "Days to Craft" guide on this site suggests.
Also, this jewel goes for 40k at the auction house in Jeuno but is very rare and not worth selling because the last sale was made months ago, at least on Lakshmi. If you don't plan on leveling goldsmithing to the 90s (which is the level range required to make accessories using Spinel), then you mineswell sell it. It's surprisinlgy cheap for the highest HQ of the purple rock.