This sponge-sized brick is actually a desiccated chunk of living coral. When exposed to at least 1 gallon of water, it expands into a full-sized boulder within 1 minute. A fully expanded coral boulder is an irregular sphere 3 feet in diameter. An expanded boulder has a hardness of 7, has 55 hit points, and weighs 8 pounds. The water in a coral boulder slowly evaporates if it's left in a dry environment, and the boulder shrinks back to its original size in about a week. If dropped in water, a coral boulder sinks straight down, and is not moved by tides or flowing water.
- Dungeoneer's Handbook
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