Enhydro is the term for a rare type of mineral that contains water inside. Enhydro minerals form in volcanic stones, such as agates, geodes, and various types of crystals, such as amethyst or quartz.
Typically these stones will have an air bubble that will move within the water inclusion. Shining a light through your enhydro mineral may make this bubble easier to find. Because the cavity is not full, enhydro stones can produce sound when shaken.
Enhydro pieces are prized by collectors due to their rarity.