Salt water is evaporated in pools to leave sea salt behind. Crushed black lava and activated black charcoal are then added for colour.
Hawaiian Black Lava Salt is a finishing salt, much in vogue with foodies these days (2004.)
Don’t use in cooking; if you stir Hawaiian Black Lava Salt into a glass of water, all the salt will dissolve and the added black elements in the salt will simply settle to the bottom as residue. The same thing would happen in cooking, so the dramatic black effect would be lost. Use only as a finishing salt at the table.