Science yields clues to an ancient salt mine

Two Experiments Help Solve a Mystery

“Residents mined and traded salt” The sign offered little information, but I wanted to know more. Ruins of an ancient Anasazi settlement were huddled into a cliff above a sinkhole full of green water and leeches. “Where did they mine salt?” I asked a ranger. He directed me to nearby Camp Verde. “Look for Salt Mine Road and just keep driving. You’ll see white mounds.” So I was off.

Cliff Dwellings Montezuma Well, New Mexico

These mounds had been worked in historic times. Lumber and twisted railroad ties lay on the ground. I strode up the mound and scooped up the white powdery material, then tasted it. It wasn’t table salt as I knew it, but did have a taste of salt mixed with … something else. Dirt was liberally mixed with the salt.  Was this material good for health? Was it sodium chloride (table salt) or something else? How was the dirt removed before eating? Or was it removed? 

Mine Workings

Crystal structure of sodium chloride could provide some clues. Common salt crystals are cubic. (Not in your salt shaker, as the crystals have been ground to a powder). As I continued to wander, I discovered a salt seep and water running from it. Where the water dropped over a rocky ledge, salty icicles hung. These were pure mineral so I broke off a few icicles and placed them in an empty coffee cup I was carrying. I would analyze these later. I peered closely at some crystal fragments drying in the sun. They weren’t cubic; the white crystals were slender needles. By the way, exploring can be messy. My feet sank unexpectedly into deep goo near the salt creek, leaving my shoe behind. I dug around for it; then walked back to my car with mud peeling off my legs. I washed off in what happened to be a historic irrigation ditch down the road.

I washed off in the Camp Verde Ditch

Experiment: grow crystals

Here’s how to analyze those crystals and discover what they might be. You can do this experiment with many common substances: salt, epsom salts, sugar. Dissolve clean grains in pure water. Start with 1/2 cup of water and dissolve as much powder as the water will take. If you heat the water first, you will be able to dissolve more powder because hot water dissolves salts more easily. Stir until theThen pour the solution onto a cookie sheet with rims to keep it from running off. If you line the cookie sheet with black construction paper, the crystals will be more visible but that’s optional. Put the cookie sheet near a window where it will get indirect sunlight and wait for the water to evaporate. Crystals will be left behind. I learned the hard way not to put the cookie sheet under direct hot sunlight. Evaporation will proceed so rapidly that good crystals don’t have time to grow. But this could be another experiment! Put one tray in the heat of summer sun and another in bright but indirect light near a window. Compare the two.

Observe the shape of the crystals. If they’re cubic, you have sodium chloride. If it’s needles, you may have magnesium sulfate. (epsom salts).

Magnesium Sulfate Crystals

Experiment: Clean dirty salt

If you don’t have clean crystals, you’ll have to remove the dirt first. How to do this? Dissolve the material, dirt and all, in water and pour it through a filter. I use paper towels or cloth in a colander. Then you can proceed as above.¬†You can also try growing crystals using dirty salt/powder. How are they different from the cleaned substance?

How did the ancient Anasazi clean the salt? They had no paper towels, colanders, and possibly no cloth as we know it. Think about this. Perhaps they let the “salt” water solution sit in a pot until the dirt settled out, then poured off the liquid for evaporation. Did they have flat stones for an evaporative surface? Or did they mix the salty solution into their foods? Or eat the salt with the dirt included?

What were the effects of eating magnesium sulfate? This mineral is actually important for many cellular functions and is sometimes used as a laxative. There are rarely negative side effects from eating it, but using it in place of salt may have left a salt deficiency in Anasazi diets. Sodium chloride is vitally important for survival. If they weren’t getting it from the “salt” mine, what other sources of salt were available? Meat and blood are one source. Some desert plants contain salt.

NOTE: The term Anasazi is outdated, but I use it here because it is still widely understood. Today’s Hopi Indians are descendants of the “Anasazi” so ancestral Hopi is a better description of cliff dwellers at Montezuma’s Well.

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