they're not rare, De Beers manually controls the market price by limiting the amount of diamonds on the market.

[u/valsagan]

[u/Redbound]

He's the wizard that created the spells. You totally could cast them without diamonds if you just altered the formula or phrasing, but he happens to own a pocket dimension full of diamonds

[u/Antique_Tennis_2500 → u/Redbound]

Society has come to expect you use the spell that requires a diamond. “I know we could revivify with a sapphire, but I’ve always wanted to do it with a diamond.”

[u/RazilDazil → u/Redbound]

And everyone thinks the spells destroy the diamonds but they really teleport them back to the pocket dimension

[u/ClearPerception7844 → u/Redbound]

So basically acquisitions incorporated spells