Mermaid's tears are a form of currency found in the underwater section of Fossil Island. They can be obtained by looting various chests and clams around the eastern part under the water.
Mermaid tears can be exchanged for items in Mairin's Market, such as unidentified fossils, a merfolk trident, bowls of fish, or seaweed spores.
Relating it to the Merfolk trident which costs 709,454 on GE, the theoretical value of one Mermaid tear could be assumed to be 1,773.
Upon reaching 0% oxygen, a random amount of tears between 10 and 20 will be lost, regardless of how many tears the players have in their inventory at the time.
- Speaking with Mairin reveals that mermaid tears are actually pearls which is why they don't dissolve in water.