Sendha namak, a type of salt, is formed when salt water from a sea or lake evaporates and leaves behind colorful crystals of sodium chloride.

It’s also called halite, saindhava lavana, or rock salt.

Himalayan pink salt is one of the best known types of rock salt, but several other varieties exist.

Sendha namak is highly valued in Ayurveda, a system of alternative medicine originating in India. According to this tradition, rock salts offer numerous health benefits, such as treating colds and coughs, as well as aiding digestion and eyesight

Rock salt can be found all over the world. There are deposits ringing dry lake beds, inland marginal seas, and enclosed bays and estuaries in arid regions of the world. At various times in the geologic past, very large bodies of water (such as the Mediterranean Sea and a huge body of water that sat where the Atlantic Ocean sits now) also evaporated and made enormous deposits of rock salt. These deposits were later buried by marine sediments, but since halite is less dense than the materials that make up the overlying sediments, the salt beds often “punched up” through the sediments to create dome-like structures. These are now mostly buried by additional sediments

Rock salt was first discovered in Winsford in Cheshire in 1844, which is the mine used by Online Rock Salt. Local prospectors were originally searching for coal – which, ironically, would be used to heat the brine-filled pans that made salt. The value of their find did not go unnoticed, however, and during the nineteenth century mining methods led to one million tonnes of rock salt being mined between 1844 and 1892.

Mining methods were still relatively basic in this era, however. Shovels, hand picks and black powder explosives were used to excavate the rock, which was then transported to the surface in wooden barrels. The work was back-breaking and often dark and uncomfortable. Up until the introduction of electricity to the mine in the 1930s tallow candles were stuck to the rock and used to light the working face. Bundles of unused candles can still be found in the old cavities of the mine to this day.

Kala namak is used extensively in South Asian cuisines of India, Bangladesh and Nepal as a condiment or added to chaats, chutneys, salads, all kinds of fruits, raitas and many other savory Indian snacks. Chaat masala, an Indian spice blend, is dependent upon black salt for its characteristic sulfurous hard-boiled-egg aroma.

Those who are not accustomed to black salt often describe the smell as similar to rotten eggs. Black salt is sometimes used sparingly as a topping for fruits or in snacks in Pakistan.