As it should, diamonds were made artificially scarce and controlled by monopoly:

“The major investors in the diamond mines realized that they had no alternative but to merge their interests into a single entity that would be powerful enough to control production and perpetuate the illusion of scarcity of diamonds. The instrument they created, in 1888, was called De Beers Consolidated Mines, Ltd., incorporated in South Africa…” From the classic 80s article “Have you ever tried to sell a diamond” - https://www.theatlantic.com/magazine/archive/1982/02/have-yo...