CleveraptorYes, but unfortunately you must narrow down further, as the question referred to a singular choice. Difficult, I know, although that is part of this inquiry, @KimHanuel. This in mind, I appreciate the elaboration but we must reach the point where the choice is not quite so simple, which is some of the fun.
Hmm...well, I guess I also chose gemstones because they come in various shapes and sizes. Just as well, they come in different...well, gems. Some examples are turquoise, hematite, chrysocolla, tigers-eye, quartz, etc. When I think of metal, I typically think of the dark grey type. It never really changes, and it stays the same. For me, going into a deeper perspective as far as gemstones go, they can change a bit. To me, sometimes change is a good thing, but it can also be a bad thing depending on the circumstances. Life is all about change and self awareness, but there's also a lot of beautiful moments. That's why I chose gemstones over metal. Change and beauty, plain and simple.