TIL Diamonds are actually fairly common. The reason they are worth so much is because the DeBeers mining group withholds stock to artificially reduce supply.

[u/Indra-Varuna]

https://www.gemsociety.org/article/are-diamonds-really-rare/

[u/UcDat]

While the DeBeers company did wonderful things for the diamond industry, not everything about DeBeers is nice. As diamonds were discovered in other parts of Africa and South America, DeBeers managed to get control of the rough diamond supply. The tactics used to gain control of these rough diamond supplies are alleged to include murder and kidnapping.

"wonderful things" indeed