Did you know that a mineral you eat every day was once so rare, it was worth its weight in gold? Wish you lived in those days? Think again. Wars were fought over it, people were enslaved to mine it, and thousands died without it.
Is your salt shaker worth that much to you?
Today salt is so common it’s in everyone’s home, but in the past salt was hard to get. The earliest civilizations developed in the few places where salt was found in the Earth. Salt, as much as gold, shaped the paths of human history. The word “salary” comes from the Latin word for salt—Roman soldiers were paid in salt as well as gold.
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Where does salt come from?
Salt forms when sodium (Na) and chloride (Cl) ions bond as a crystal (NaCl). The ocean is salty, because water dissolves these ions from rocks over time. Salt “beds” form from ancient, dried-up seas. Some are thousands of feet thick and can be buried deep underground. Salt can also crystallize into spectacular formations when volcanic gases bubble through water.
The dry air of deserts can pull salt to the surface to form a crust, and salt springs can gush natural saltwater.
Since prehistory, people have collected salt from these sources. But when salt wasn’t available, people gathered plants high in salt and—as a last resort—ate dirt with salt in it. Animals need salt, too, so salt licks attract wildlife.
Why is salt so important to humans?
Salt is critical for our health. But because our bodies can’t make it, we have to eat it. Salt is so important that our cells won’t work without it. Salt helps blood pump, and muscles and nerves move. Careful, though! Oversalting food can be unhealthy. Most of us eat much more than we need―about 2/3 of a teaspoon per day―from packaged and processed foods.
How did salt shape human history?
Civilizations thrived where salt was found, and fought to own it.
Empires rose and fell around salt. For sixteen centuries, salt from the African Sahara incited wars, robbery, murder, and slavery. Salt was in such demand that caravans of up to 3,000 camels (each animal carrying 400 pounds of salt) traversed the barren sand dunes of the Sahara to inland civilizations. Salt was so precious to West Africans, they traded a pound of gold for a pound of salt.
For hundreds of years the British Empire controlled salt in India, keeping the price so high that many people couldn’t afford it and died from lack of salt. As recently as 1930, Gandhi rallied the Indian people to defy Britain’s salt control with his famous ‘salt march’ to the sea to illegally harvest the sea salt they desperately needed.
Romans used salt from the Mediterranean, but they relied on salt mines in Europe, too. The Wieliczka Salt Mine in Poland is a deep bed of salt that has been mined for table salt since the 13th century. Carved by miners into spectacular underground chapels, ballrooms, altars, and sculptures on nine levels, it is now preserved as a much-visited World Heritage Site.
Is salt used for anything besides food?
Outside the salt shaker, salt has many other roles. Salt is used for curing meats, de-icing roads, fixing dyes in clothing, making paper and plastic, and treating city drinking water. Also, oil companies know to look for crude oil trapped by underground salt formations. Some deeply buried salt beds are being used to store hazardous waste.
Next time you reach for the salt shaker, think about how this simple mineral you eat every day has shaped human history. If salt was still worth its weight in gold, your 2-ounce salt shaker would cost over $4,000.
Make salt crystals from your own salt pond!
Native Ohlone people collected salt near San Francisco Bay using willow sticks they stuck into salt ponds, letting the sun evaporate seawater and form crystals. The sticks could be stored easily and transported for trade.
Here’s a way you can extract salt using a bowl as the shallow pond and toothpicks to collect the salt.
• Modeling clay
1. Pour hot water into a bowl to cover the bottom about an inch.
2. Add a tablespoon of salt and stir until it is dissolved.
3. Continue adding salt until no more salt will dissolve.
4. Make small balls with clay and stick them to the bottom of the bowl.
5. Put a toothpick upright in each ball of clay.
6. Set the bowl in a warm area so the water evaporates.
7. Crystals will grow on the sticks within a day and keep growing!
Salt as an earth mineral
Tikkanen, A. Encyclopaedia Britannica. Halite. https://www.britannica.com/science/halite Accessed 3/9/22
Debure, M., Lassin, A., Marty, N.C. et al. Thermodynamic evidence of giant salt deposit formation by serpentinization: an alternative mechanism to solar evaporation. Nature Sci Rep 9, 11720 (2019). https://doi.org/10.1038/s41598-019-48138-9
Salt of the Earth. Bennett, H. 2019. BBC Science Focus Magazine. https://www.sciencefocus.com/planet-earth/salt-of-the-earth/ Accessed 2/2/22
What is a salt dome? Geology.com article. https://geology.com/stories/13/salt-domes/ Accessed 2/1 2022.
Salt Tectonics. Wikipedia. https://en.wikipedia.org/wiki/Salt_tectonics Accessed 2/4/22
Salt and health
Mayo Clinic. Sodium: how to tame your salt habit. https://www.mayoclinic.org/healthy-lifestyle/nutrition-and-healthy-eating/in-depth/sodium/art-20045479 Accessed 2/8/22
American Heart Association. How much sodium should I eat per day? https://www.heart.org/en/healthy-living/healthy-eating/eat-smart/sodium/how-much-sodium-should-i-eat-per-day Accessed 2/8/22.
Salt and human history
Interviews with research biogeochemist Robert Stallard, PhD, researching salt history and biogeochemistry in Amazonia. US Geological Survey. November 20, 2021; January 28, 2022.
Interview with Kathy Strain, MA, Forest Heritage Resource and Tribal Relations Program Manager, Forest Service, Stanislaus National Forest. November 15, 2021.
The salt trade of ancient West Africa. Mark Cartwright. 2019. https://www.worldhistory.org/article/1342/the-salt-trade-of-ancient-west-africa/ Accessed 2/3/22
Salt. Hesham Najiya and Jason Cole, University of Waterloo Earth Sciences Museum. https://uwaterloo.ca/earth-sciences-museum/resources/detailed-rocks-and-minerals-articles/salt Accessed 2/3/22.
Salt on a stick experiment
Kids Earth Science. https://www.kids-earth-science.com/water-cycle-experiment.html Accessed 2/2/22.
Salt Ponds and Marshes of the San Francisco Bay Area. Katie Gu, David Chen, and Ethan Li. https://microcosmos.foldscope.com/?p=146651 Accessed 2/8/22.