The Dietary Minerals
Life makes use of just a handful of the 92 naturally occurring elements. The overwhelming majority of our substance consists of carbon and the three gases oxygen, nitrogen and hydrogen. Everything else, about a dozen different elements, is "minerals." So-called major minerals are needed every day in significant amounts—humans need quantities on the order of a gram. They are
- Calcium
- Chlorine
- Magnesium
- Phosphorus
- Potassium
- Sodium
The minor or trace minerals are needed in microscopic amounts:
- Chromium
- Copper
- Fluorine
- Iodine
- Iron
- Manganese
- Molybdenum
- Selenium
- Zinc
There are other elements that occur in living tissues but are rarely a worry because they're so widespread in the diet or the environment:
- Boron
- Cobalt
- Nickel
- Strontium
- Sulfur
Dietary Minerals Are Ions
In every case, our bodies use the dietary minerals not as pure elements, but as ions, or atoms with charge. Charge—an excess or deficiency of valence electrons—is what makes chemistry of all kinds work. Because life operates in water, everything dissolved in it turns to ions. Think of the water environment as a giant dance floor, and the "minerals" that dissolve in it as dancers who are locked off of it until they move to the beat.
The calcium sheds its two loosest electrons to become the positive ion Ca2+. Chlorine grabs an extra one to become the chloride ion Cl-1. And so on. Some elements are so highly charged, like phosphorus, that their most stable configuration in water is as the big phosphate ion PO43-. (Chemistry Guide Anne Helmenstine has a handy list of such polyatomic ions.)
In any case, the dietary minerals are of no use to life until they're dancing around in ionic form, ready to partner up with ions of opposite charge. This is why geologists can't picture dietary minerals as real minerals. Real minerals are solids with precise chemical recipes and crystalline arrangements. Dietary minerals are just inorganic ions doing a chemical boogie. And most real minerals don't dissolve in water very well. Over billions of years, life on Earth has evolved enzymes that can crack open mineral molecules to release the right ions—and they're working in your body right now. The study of how life and minerals interact is biogeochemistry, one of Earth science's most exciting fields today.
Could Real Minerals Supply Dietary Minerals?
There is one true mineral that we eat: salt, the mineral halite, is a compound of two major nutrients, sodium and chlorine. But in all the other cases, we can't get our minerals from real minerals. Think how convenient it would be to get our minerals by eating rocks! However, these "mineral minerals" would have to be softer than our teeth, which are Mohs hardness 5:
- Boron would come from a nibble of ulexite, if we really needed any.
- Calcium would come from calcite or gypsum.
- Chromium would come from a smidgen of fuchsite or mariposite.
- Cobalt is an impurity in several different sulfide minerals, although you'd have to watch for arsenic too.
- Copper would come from chrysocolla or malachite, although we could probably gnaw on native copper if we had to.
- Fluorine would come from fluorite, just a little bit because it would be easy to overdose.
- Iodine is too rare in minerals to use this way; better to stick to seaweed if you need any at all.
- Iron would come from limonite, although siderite would be a lot more appetizing. (Hematite would be too hard.)
- Magnesium would come from dolomite, with the benefit of supplying calcium too.
- Manganese would come from rhodochrosite, of course.
- Molybdenum would come from a tiny flake of molybdenite.
- Nickel is everywhere that iron is, so that wouldn't be a problem.
- Phosphorus would come from variscite. Apatite would be simpler, but apatite is what composes our teeth so they would probably wear out quickly.
- Potassium would come from sylvite (though that's quite bitter). Potassium feldspar is millions of times more common, but it's hardness 6.
- Selenium is like iodine, almost never found in mineral form. For that we'd have to have it as an impurity in a sulfide source, or just continue relying on food.
- Strontium would come from celestine, if we needed any beyond what's present as an impurity in other minerals.
- Sulfur would be easiest to get from gypsum, but native sulfur is certainly possible too.
- Zinc would come from sphalerite or smithsonite.
On the whole, I like the current system of getting our minerals, even if they aren't real minerals.
