2). “Investment-grade diamonds hardly exist, therefore diamonds are not a good investment” - Myth
A good amount of investment-grade diamonds exist. It is very difficult to find them, though, as diamonds lack fungibility and typically the choice of investment would boil down to either spending a lot of time trying to find the best investment-grade diamond on your own and get a higher annual return, or go to more standardised assets (like oil and gold) which give a lower annual return.
Companies like ECN Investments however, are putting a third option into the mix - to find the investment-grade diamond so you don’t have to, allowing you to profit from the higher annual returns in diamonds.