Indian black salt, or "Kala namak," is a volcanic salt used primarily in Indian and Pakistani cuisine. It's known as black salt, even though it appears pink, because before grinding it consists of pinkish-gray crystals, its color due to its high iron content and other minerals. Once ground, it takes on its characteristic pale pink hue.
One of the characteristics of this salt is that it has a strong 'sulfurous' flavor, which makes us think of a fried or boiled egg on the palate; that's why this salt is called egg-flavored salt.