I would be skeptical of placing too much confidence in precious metals as a long-term (say, twenty-year) hedge against inflation or economic or political turmoil, due to the possibility of creating or extracting synthetic precious metals. The old dream of the medieval alchemists has been achieved. At the moment, synthetic gold is not economically viable, but who knows what the future may bring.
Precious stones are already being synthesized in an economic fashion. I purchased a four-carat synthetic blue sapphire for my mother ten years ago.