Today, global diamond deposits are increasingly becoming depleted. Less than 20% of the diamonds mined are of gem quality and less than 2% are considered investment-grade.
75-80% of mined diamonds are used for industrial applications, such as grinding, sawing, and drilling. Typically, more than 250 tons of ore must be mined in order to produce a one-carat, gem-quality diamond.
The formation of diamonds can be said to be unpredictable in nature, and there is no guarantee that more diamonds can be formed during this lifetime.
The conclusion from the above is that investment-grade diamonds are rare. And rarity has a positive correlation with value.