A Pirate´s Word

From BoardGameGeek:

Centuries ago, the legendary Blackbeard sailed the seas, leaving behind a treasure so vast it was nearly impossible to hide. Nowadays, gems of immeasurable value appear daily on the nearby islands. You've come seeking riches-but you're not the only greedy pirate on the island. The game lasts five Days. Each day, new Gems are placed on the Islands, which sit between each pair of players. Everyone has 3 cards in hand: 2 green (for cooperation) and 1 red (for betrayal). You'll secretly choose one card to place face down on the Island to your left, and another on the one to your right. If both players choose green, they split the Gems. If one goes green and the other red, the red player takes all the Gems. But if both play red, no one gets anything. Everything is up for negotiation-but will you trust a pirate's word? -description from the publisher