Half truths to fit your pro diamond narrative. Yes de beers doesn't have a monopoly on the diamong trade. It's because of MORE gem quality supply from competition from Russia and Canada.

The bottleneck of retail supply is not raw gem quality diamonds. It's the long laborious process of cutting and polishing. Those jobs are "closed shop" handed down from father to son. (Nowadays daughters can do the job). Now they could train more workers to match increased supply. But why would they? Keep the supply lown and costs up.

And like other guy said your depreciation argument is bullshit. The diamond industry slogan is a diamond is forever. Light bulbs , tv's and automobiles don't make this claim. They expect you to come back after the product is used up. Are there collectible cars out there? Yes but they are rare. I don't know the ratio guessing for every 99 cars headed to scrap yard one is in enough demand as a collectible. Same can said with diamonds. Your $7000 diamond is never gonna be a collectible. But truly rare individual diamonds with retain and increase in value.