Salt Questions · Science, chemistry & environment
What is rock salt made of?
Short answer
Rock salt is the mineral halite: sodium chloride that crystallised from ancient seas and lakes and was buried underground. It is usually more than 95% sodium chloride, with small amounts of clay, gypsum, anhydrite and other minerals that can colour it grey, brown, pink or blue. It's mined for road salt, water softening and food.
Typical road-grade rock salt (approximate)
- Sodium chloride (halite) 96%
- Clay, gypsum and other minerals 4%
The mineral halite
Halite is the mineral name for natural sodium chloride. Pure halite is colourless and transparent, forming cubic crystals.
Why rock salt isn't pure white
- Clay and sediment: grey or brown tints, common in road salt.
- Iron oxide: pink to red, as in Himalayan salt.
- Radiation damage to the crystal lattice: rare blue and purple halite.
Uses
| Roads | Crushed rock salt for de-icing, often with an anti-caking agent |
|---|---|
| Food | Purified or food-grade rock salt, such as Himalayan salt |
| Industry | A raw material for chlorine and sodium hydroxide |
Related on The Salt Almanac
More science, chemistry & environment questions
- How does salt water affect the density of water?
- Why do things float easier in the Dead Sea?
- What is the difference between organic and inorganic salt in chemistry?
- What is the chemical formula for table salt?
- Why does salt melt ice on roads in the winter?
- Is salt an element, a compound, or a mixture?
Cite this page
For school projects and reports. Teachers often prefer the original sources too: see the list below.
The Salt Almanac. (2026, November 8). What is rock salt made of. https://saltalmanac.com/answers/what-is-rock-salt-made-of
“What is rock salt made of.” The Salt Almanac, 8 Nov. 2026, saltalmanac.com/answers/what-is-rock-salt-made-of. Accessed [today's date].
“What is rock salt made of.” The Salt Almanac. Last modified November 8, 2026. https://saltalmanac.com/answers/what-is-rock-salt-made-of.
Original sources
- Wikipedia. Halite. https://en.wikipedia.org/wiki/Halite