Black salt is an exotic, smoky salt from India known as Kala Namak.
Kala Namak can range from a brownish pinkish color to a dark grey. Other black salts on the market are sea salts with a carbon additive and Hawaiian Black Lava Salt.
It is mined in India and used as a condiment. In Indian cuisine it is also added to chutneys, chaats, raitas, chaat masala, and fruits. Someone who has never tasted it before will usually describe the scent as similar to that of rotten eggs.