Horn coral

Horn coral was not a mineral but a highly prized variety of coral. It was also known as night coral.

Description
The deep black version of horn coral was similar to angelar's skin except for its solid color. It was polished and used in jewelry, typically cut cabochon or left in its twig and branch form. A typical specimen had a base value of 500 gp.

Powers
Horn coral had the unique property of granting water walk to someone wearing the item. To release this power, the wearer had to touch the horn coral with one of their own tears and call on the ability. The effect lasted up to an hour, after which, the horn coral disintegrated into dust. A few rare specimens did not dissolve and could be reused after about ten minutes. There was no known method of distinguishing which specimens would not be consumed by casting water walk except by trial.

Trivia
The lesser deity Vhaeraun was known to occasionally send horn corals to show his favour or disfavour to his followers.