Because of the presence of greigite (Fe3S4, Iron(II,III) sulphide) in the mineral, it forms brownish-pink to dark violet translucent crystals when whole.

[6] This involves firing the raw salts in a kiln or furnace for 24 hours while sealed in a ceramic jar with charcoal along with small quantities of harad seeds, amla, bahera, babul bark, or natron.

[4] Although hydrogen sulphide is toxic in high concentrations, the amount present in kala namak used in food is small and thus its effects on health are negligible.

[4] Kala namak is used extensively in South Asian cuisines of India, Pakistan, Bangladesh, and Nepal as a condiment or added to chaats, chutneys, salads, fruit, raitas, and many other savory snacks.

Chaat masala, a South Asian spice blend, is dependent upon black salt for its characteristic sulphurous egg-like aroma.

In the United States, the Food and Drug Administration warned a manufacturer of dietary supplements, including one consisting of Himalayan salt, to discontinue marketing the products using unproven claims of health benefits.