One of the rarest salts I have come across in my research is Asin Tibuok sa Albur, or “Unbroken Salt of Albuquerque” which is an artisanal sea salt produced by traditional methods in the small town of Albuquerque on the island of Bohol, Philippines. It is so rare because of its long, involved process that has to lead to its near vanquish; only three families (or less by now) are known to produce this salt. (Also named “The Dinosaur Egg” because of its shape and nearly obsolete age-old process.) This salt was inducted into the Slow Food Ark of Taste in 2016.
The process begins by building a pit on the shore of the beach to catch seawater as the tide comes in. Dried husks of coconut are soaked in the saltwater pit for a month so that the husks retain as much salt and minerals as possible. Then the husks are dried in the sun for a few days, cut into smaller pieces, and roasted over an open fire for hours until they turn to ashes. Afterward, they are mixed with more seawater to form a liquid. Then the liquid is placed into small terracotta pots that are hung over a concentrated fire of pinewood. As the liquid evaporates, more is placed inside the pots. When the pots are completely full of hardened salt, the pots crack across the bottom and the process is complete.

The salt produced by this method is a pale pinkish-white in color, and it retains a smoky flavor from the firing processes with a hint of sweet taste from the coconut husks. As you can imagine, it contains a great number of nutrients from the concentrated sea minerals, the ash from the firing process, and the clay deposits from the pots it is boiled in. Native people use this salt primarily as curing and/or finishing salt for fish, but it is also used as a (rather expensive) kitchen salt. Can you imagine the flavor this salt would impart on a juicy slice of tomato?