Technically speaking, gold per se can hardly be considered as an investment

Investing assumes gaining profits over time, while gold doesn't fit quite well into this scheme. It is rather an instrument of storing or preserving value and wealth (so-called a store of value of last resort), not an asset which allows you to earn profits over long term (unlike, for example, the US Treasury bonds). This has nothing to do with short term speculations, though, in which gold can be used successfully, for example, with gold futures and options (if you know what you are doing, of course), but such speculations cannot be called investments either, at least, not in the proper sense of the word