Siren Gems are a new jewel you can locate in Sea of Thieves following the A Pirate’s Life update that came with the single-player campaign and Jack Sparrow’s adventure. Much like the regular gems you can find in Sea of Thieves, there are three types: a Sapphire Siren Gem, an Emerald Siren Gem, and a Ruby Siren Gem. Each of the gems provides you with a decent gold reward when you bring it back to an outpost to sell.
Finding these gems can be a bit tricky, but there are a handful of ways to locate them. The two quickest ways is to locate them on Sirens or on Ocean Crawlers. Both of these are enemies introduced in A Pirate’s Life update. Sirens are ocean-dwelling creatures that you can find when you dive straight into the water. Once you hear their song, you’ll know they’re coming after you, and defeating them in their territory can be tricky. The Ocean Crawlers will appear on land, similarly to as if they were skeletons, and there are three types that you have the chance to defeat. All have the same chance of dropping a Siren Gem.
These are the only two methods that we know that you can acquire these Siren Gems. They’re both tied to A Pirate’s Life update. We could likely see chests appearing in the future that contains Siren Gems, but for now, you’ll have to do battle against these new creatures if you want to add a Siren’s Gem to your collection and offer it to a trading company of your choice.