Obtaining Diamonds
Diamonds can be obtained by completing some prophecies from the Fated List of Minor Prophecies. They can also be obtained via trades with the Wretched Broker.
Diamonds are primarily earned by beating the Lernaean Bone Hydra and collecting a Bounty for escaping Asphodel.
Occasionally, a Diamond can also be purchased from Charon's shop in the Temple of Styx for 1000 .
Poseidon's boon Sunken Treasure also has a 0.3% chance of dropping a Diamond.