Diamonds are not really an investment. But at least they are worth something. Keep a car long enough (unless fabulous care is taken of them) they eventually end up in the junk yard. Diamonds will always be worth something. When people speak of their re-sale value the same can be said of a car. I purchased a new SUV this year. The price was right in line with the book value. Now just 9 months later I owe 3000.00 more on that vehicle than the book value.
The other gems I mentioned not only are worth something, but usually appreciate in value---like my 10 carat deep purple tanzanite I got a 'bzillion years ago....it's worth 6 times more than I paid for it, if I wanted to sell it.
I'd rather wear it.
Same with black opals too....
Oh yeah,
and things like cars, clothes, furnishings etc...
Goodwill and Salvation army....really, really old, beat up and cheap.