Halite (Rock Salt)
Halite is the mineral form of salt. Every grain of edible salt on earth — table salt, sea salt, kosher salt, Himalayan pink salt — is halite, or was halite before it was dissolved and recrystallized. The name comes from the Greek hals ("salt") and lithos ("stone"). Chemists call the same substance sodium chloride and write it NaCl; geologists call the naturally formed crystal halite; cooks call the refined product salt. One material, three vocabularies.
Composition: What Salt Is Actually Made Of
Halite is an ionic compound, not a molecule. Sodium gives up one electron to become Na+; chlorine accepts it to become Cl−; the two ions then hold each other in place by electrostatic attraction. By mass, pure halite is 39.34% sodium and 60.66% chlorine — which is where the everyday conversion factor comes from: multiply grams of salt by 0.393 to get grams of sodium, or divide milligrams of sodium by 2.5 to get milligrams of salt. Our salt to sodium calculator does this for any amount.
Because there are no discrete NaCl molecules, a halite crystal is best described as one enormous repeating lattice. That structure explains nearly every property salt has:
| Property | Value | Why |
|---|---|---|
| Crystal habit | Cubes, occasionally hopper-shaped | Ions stack in a face-centered cubic array |
| Cleavage | Perfect in three directions at 90° | Lattice planes separate cleanly along cube faces |
| Mohs hardness | 2.5 — scratched by a fingernail with effort | Ionic bonds are strong but brittle |
| Melting point | 801°C (1,474°F) | Breaking the full lattice takes considerable energy |
| Solubility | ~359 g/L in water at 20°C | Water molecules pull individual ions away from the lattice |
| Taste | Salty | Na+ ions activate the ENaC channels on the tongue |
| Color | Colorless or white when pure | Impurities and lattice defects produce pink, grey, blue or orange |
Halite vs Rock Salt: Is Salt a Rock or a Mineral?
Both, depending on the scale you are looking at. Halite is a mineral; rock salt is a rock made of halite. A mineral is one substance with one formula and one crystal structure. A rock is an aggregate of mineral grains. A salt bed a hundred meters thick is a sedimentary rock — specifically an evaporite — and it is composed almost entirely of interlocking halite crystals, in the same way that quartzite is composed almost entirely of quartz.
In everyday use "rock salt" means something narrower: coarse, unrefined halite sold either as food-grade crystals or as de-icing salt for roads. Those two are not interchangeable, and the difference matters — see is rock salt edible? for the safety distinction.
How Halite Deposits Form
Halite is an evaporite mineral, meaning it precipitates out of evaporating brine rather than crystallizing from magma or growing under pressure. The sequence is remarkably consistent worldwide. As a body of seawater is cut off from the ocean and evaporates, the least soluble salts drop out first: carbonates, then gypsum and anhydrite at roughly 20% of the original volume, then halite at around 10%, and finally the bitter potassium and magnesium salts — sylvite, carnallite, polyhalite — in the last few percent. This is why gypsum layers almost always sit directly beneath halite beds, and why the potash minerals sit on top.
Most of the world's mined halite formed this way in shallow inland seas hundreds of millions of years ago. The Khewra deposit that produces Himalayan pink salt is roughly 600 million years old; the Cheshire and Michigan basins are Triassic and Silurian respectively. Because halite is less dense than the rock burying it and deforms plastically under pressure, thick beds can flow upward over geological time into domes and diapirs — structures that trap oil and gas above them, which is why salt geology and petroleum geology are so closely linked.
Where Halite Is Found and Mined
Why Halite Comes in Colors
Pure halite is colorless and transparent; a large clean crystal looks like glass. Color arises three ways. Mineral inclusions account for most of it — iron oxide gives Himalayan salt its pink, clay and algae give sel gris its grey, and volcanic clay gives alaea salt its brick red. Lattice defects explain the rest: the deep blue of Persian blue salt is not an impurity at all but an F-centre, a gap in the lattice where a trapped electron absorbs light. Added material covers the remainder, such as the activated charcoal in black lava salt.
Crucially, none of these coloring agents is present in nutritionally meaningful quantity. A colored halite is still 97-99% NaCl by weight.
From Mineral to Table Salt
The halite that reaches a kitchen has usually been processed. Mined rock salt is crushed, dissolved into brine, filtered to remove insoluble rock, then re-evaporated in vacuum pans to produce the small uniform cubes sold as table salt. Anti-caking agents and, in most countries, potassium iodide are added afterwards. Unrefined salts skip most of these steps, which is the entire difference between them and refined salt — not a difference in the mineral itself.
| Halite (natural) | Table salt (processed) | |
|---|---|---|
| Composition | NaCl with variable natural impurities | 97-99% NaCl plus additives |
| Crystal form | Cubes up to several centimeters | Uniform cubes around 0.3mm |
| Additives | None | Iodine, anti-caking agents, sometimes dextrose |
| Density in a spoon | Varies with grain size | ~6.0g per teaspoon |
Related Minerals
Halite rarely occurs alone. Sylvite (KCl) is its potassium analog and the main ore of potash; it looks nearly identical but tastes bitter. Carnallite (KMgCl₃·6H₂O) and polyhalite form in the same final stage of evaporation. Gypsum (CaSO₄·2H₂O) and anhydrite (CaSO₄) precipitate earlier and are the usual floor of a halite bed. Together these make up the evaporite mineral group.