From the publisher's website:

Diamonds is a trick-taking card game in which players collect Diamonds — not cards bearing that suit, mind you, but rather actual "Diamond Crystals" (acrylic crystals) included in the game. What makes the game of Diamonds different from other trick-taking card games is that when you cannot follow suit you get a "Suit Action" based on what suit you do play. Suit Actions are also taken by the winner of each trick, as well as at the end of a full Round of play. Suit Actions will enable players to take Diamond Crystals from the Supply, moving them to their Showroom (where they may score 1 point) or to their Vault (where they will score 2 points). The Vault is a secure area, but the Showroom is vulnerable to theft by the other players. Whoever has the most points in Diamond Crystals at the end of the game wins! Diamonds features great components, great gameplay, and stunning Art Deco stying with metallic gold and silver inks.