[meow_meow]

So, if I understand all of your post correctly, you are looking to invest in something tangible - metal, gems, etc..., but which doesn't require a lot of specialized knowledge. Further, you would like it to be at least moderately easy to liquidate and you want a reasonable shot at an ROI greater than inflation over the next 10-20 years.
Does that about sum it up?

That's a pretty tall order. Actually making money in any kind of collectable (art, stamps, cards, elvis toenail clippings, etc..) does require study and specialized knowledge. I imagine that this goes for gemstones as well.

I'm curious as to why market instruments are so unappealing to you, as the enormous array of options is guaranteed to fit any risk profile...

If you are looking for something that will have a good chance of maintaining value no matter what happens, or that you could stash or take with you if you need to leave everything behind, then I hate to say it but gold is the way to go. Good value to weight ratio, people will always value it, despite the dearth of industrial uses.

If you are looking to make good returns with a minimum of risk, then you really can't do better than the stock market, especially if you aren't willing to devote a lot of time and effort in specialized knowledge.