The Rocks We Eat

The foods and beverages we eat and drink all have different phases: solid, liquid, and gas. (How do we ingest gases? Carbonated beverages have gas, which sometimes cause a person to belch.) However, among the solids we eat, three in particular are, or are produced from, rocks. Yes, rocks!

The first one is NaCl, or common salt. Salt is the only solid that we ingest that is actually mined as a rock (hence the term rock salt; it really is a rock). Salt provides both Na⁺ ions and Cl⁻ ions, both of which are necessary for good health. Salt preserves food, a function that was much more important before the days of modern food preparation and storage. The fact that saltiness is one of the major tastes the tongue can detect suggests a strong evolutionary link between ingesting salt and survival. There is some concern today that there is too much salt in the diet; it is estimated that the average person consumes at least three times as much salt daily than is necessary for proper bodily function.

The other two rocks we eat are related: sodium bicarbonate (NaHCO₃) and sodium carbonate (Na₂CO₃). However, we do not mine these substances directly from the ground; we mine trona, whose chemical formula is Na₃H(CO₃)₂. This substance is dissolved in water and treated with CO₂ gas to make either Na₂CO₃ or NaHCO₃. Another process, called the Solvay process, is also used to make Na₂CO₃. In the Solvay process, NH₃ and CO₂ are added to solutions of NaCl to make NaHCO₃ and NH₄Cl; the NaHCO₃ precipitates and is heated to produce Na₂CO₃. Either way, we get these two products from the ground (i.e., rocks).

NaHCO₃ is also known as baking soda, which is used in many baked goods. Na₂CO₃ is used in foods to regulate the acid balance. It is also used in laundry (where it is called washing soda) to interact with other ions in water that tend to reduce detergent efficiency.