Kala Namak is also commonly called black salt, or Himalayan black salt. It contains sulfur compounds that give it a slight "eggy" taste and smell. The salt it typically black, gray, or brown in color. It's often used in vegan dishes meant to mimic eggs because of its taste. Kala namak is often used in Indian cooking, so you can purchase it at any Indian grocer. It can also be purchased at online retailers like Amazon.