Rock Salt vs. Table Salt: Grain, Iodine and the Bag That Isn’t Food

Rock salt and table salt are closer relatives than they look. Rock salt is salt mined from underground deposits, and table salt is salt mined from deposits and then processed to a fine texture. The real differences come down to the grain, what’s added to the box, and iodine. Watch for one practical trap, too: a lot of the coarse “rock salt” sold in American stores is ice cream or de-icing salt, and Morton says it’s not intended for consumption.¹

Side by side

Food-grade or not

Morton sells its Ice Cream Salt as large rock salt crystals that cool gradually in ice cream makers and coolers. It lists melting ice and snow among the uses and says it’s not intended for consumption.¹ In 2024, highway deicing took about 41% of all the salt consumed in the US.⁷ So only cook with rock salt when the package says it’s food grade, or it carries a nutrition panel and is sold as a cooking salt. We found no regulator data on what non-food rock salt contains. That makes this a labeling rule, not a claim that the stuff is harmful. More at rock salt.

Where each comes from

The Codex standard for food-grade salt covers salt from the sea, from rock salt deposits and from natural brine. It requires at least 97% sodium chloride on a dry basis, not counting additives.⁸ By that measure, the two are the same substance. Rock salt is a big slice of the US supply: in 2024 it made up 40% of salt sold or used, against 42% salt in brine, 9% solar salt and 9% vacuum pan salt.⁷

Table salt is defined more by how it’s processed than where it comes from. Its tiny, uniform crystals come from rapid vacuum evaporation, and it usually carries an anticaking agent so it pours smoothly. The AHA says the processing strips out other minerals.⁶

What’s added to table salt

Morton’s iodized table salt lists salt, calcium silicate (an anticaking agent), dextrose and potassium iodide.³ Under US rules, salt with added iodide may be labeled “iodized salt” and must say it supplies iodide, a necessary nutrient. Salt with an anticaking agent may be labeled “free flowing.”⁹ US salt makers have added iodine since the 1920s, and it’s voluntary.⁴

You’ll often hear that these additives make table salt taste faintly bitter. America’s Test Kitchen’s tasters couldn’t detect any difference in taste between iodized and noniodized salt.² We found no source on whether food-grade rock salts in general carry additives, so we won’t call them additive-free. Read the label.

Minerals, measured

A 2016 Swiss government survey of 25 retail salts included one iodized table salt and four Himalaya salts, which are rock salts. The comparison below covers those samples, not rock salt in general.¹⁰

All figures come from the FSVO report.¹⁰ It found that specialty salts generally carried more contaminants than standard salts, though most didn’t reach even 1% of tolerable intake levels. Its conclusion: specialty salts have no advantages over standard salts.

Can one stand in for the other?

In food, yes, as long as the rock salt is food grade. These swaps match our rock salt substitute page.

How we got these numbers. By weight: Codex requires at least 97% sodium chloride on a dry basis for salt from any source.⁸ By volume: Morton’s chart treats a teaspoon of its Himalayan salt as equal to a teaspoon of its table salt, for Morton products only,¹¹ and its labels give both as 1.5 g per ¼ teaspoon.⁵³ For other coarse rock salts we couldn’t find a published weight. Big crystals hold less salt per spoon only because fewer of them fit.⁶ Table salt, at about 6 g a teaspoon, is the densest of the common salts,¹² so starting at half and tasting keeps you from over-salting. For ice cream, Colorado State University Extension’s recipe calls for ½ cup of salt, “Kosher or rock salt,” and explains that salt lets the ice-and-salt mix get colder than plain ice.¹³

Which to use when

• Food-grade rock salt: salt grinders, pasta water, salt crusts and roasting beds, where coarse, hard crystals help. These are everyday kitchen uses, not tested claims.
• Table salt: anything you measure by the spoon, baking, and the shaker. Morton markets its iodized salt for cooking and baking.³
• Non-food rock salt: the ice around an ice cream canister, and the driveway.

Health notes

• Sodium. Neither one is lower in sodium by weight. Table salt, kosher salt and most sea salts are about 40% sodium.⁶ The WHO recommends adults keep sodium under 2,000 mg a day and names raised blood pressure as the main health effect.¹⁴
• Iodine. Here’s the real difference. Iodized table salt carries 45 mcg of iodine per gram, and specialty salts like Himalayan salt usually aren’t iodized.⁴ If you switch to rock salt at home and count on salt for iodine, keep iodized salt around too. See iodized vs. non-iodized salt.
• Microplastics. In a 2018 study of 39 salt brands, reported in a Greenpeace press release, the nine rock salts had the least microplastic contamination of the three types tested.¹⁵ The release doesn’t give a separate figure for table salt.

What isn’t known

• No published weight per teaspoon for coarse rock salts beyond Morton’s Himalayan label.
• No source on whether food-grade rock salts in general contain additives.
• No regulator source we found says what non-food rock salt contains beyond salt.
• No test of ice cream made with table salt in the ice bath.
• No dated, sourced price comparison.

Related

• Rock salt and table salt, the full profiles
• Rock salt substitutes
• Rock salt vs. sea salt, Himalayan salt vs. table salt and kosher salt vs. table salt
• Cooking with rock salt and the best salt for cooking