“would precious gem jewelry be of any worth?”
No. Only jewelers and gemologists would know the value of cut gemstones, and the market value would fluctuate from buyer to buyer. You can buy rough gemstones for a song. You can also pass off cheap, man-made cubic zirconia jewelry as diamond rings, pendants, etc. You can buy decent zirconia cut stones and jewelry from communist China or Thailand on eBay for a few dollars.
Don’t confuse real zircon gemstones with the man-made zirconia. They are similar in appearance but zircon is much more expensive.
https://en.wikipedia.org/wiki/Cubic_zirconia
Have fun...
That is ridiculous. There are simple tests for gems:
Market value varies on everything--that's why it's called market value. Paying retail and expecting to sell at that is rarely a good idea. That said, diamonds are a poor candidate since their value is completely and artificially set by the DeBeers cartel.
Anything you hold for contingency commerce is not an investment, but a store of value. That is, something to liquidate to good purpose--it's value dependent on time, opportunity, and need.
You may not want to sell grampa's gold watch today for a measly $500, but you would think nothing of trading it for a couple of bottles of antibiotics when your child really needed them.