The human body requires moderate amounts of seven minerals (calcium, phosphorus, potassium, sulfur, sodium, chloride, and magnesium). Trace amounts of other minerals are also required. Minerals make up about 4% of the body’s weight with calcium and phosphorus accounting for about ¾ of this amount (Marieb 1998).

These minerals are supplied from the food and liquid items we consume, as well as from sources we normally would not consider as important. Some trace minerals are incorporated in seasoning items we tend to use frequently. For example, iodine has been added to table salt since 1924 in some countries (Boyages 1993). However, there are risks and benefits to this practice (Delange 1998, Davidsson 1999).

Some cultural behaviors add earthen materials directly into their diet, perhaps as a mineral supplement (Reid 1992). For example, the eating of clay is practiced in several cultures throughout the world. Clay may be added into various foods and consumed directly for its medical qualities, or eaten during times of food scarcity (Wiley and Katz 1998). Some cultures may consume clays as an absorber of dietary, bacterial, and metabolic toxins which may cause vomiting and diarrhea if not treated properly (Reid 1992). For example, the Pomo Indians of California mixed clay with the ground meal of acorns, perhaps to absorb the bitter toxins found in acorn meal (Johns and Duquette 1991). Many clays contain sufficient amounts of minerals and may be used as a form of nutrient supplementation (Wiley and Katz 1998). Aluminum, magnesium, iron, and calcium are the common minerals found in clay.

Some minerals in clays are beneficial in terms of the uptake of cations in the diet. For example, clay can give up calcium for zinc or iron, or it can take up iron for aluminum, a non-nutritive mineral (Wiley and Katz 1998). Often, the eating of clay is called geophagy, and this practice is not restricted to humans only. Geophagy is common in birds (Diamond 1999) and the use of soils and clays in the diets of ungulate livestock is well documented (Kreulen and Jagger 1984).

At times, mineral supplementation is obtained from unintentional sources, like cookware. Depending on the cookware, iron, chromium, and nickel are all released into the food. For example, stainless steel cookware can be a source of chromium and iron (Kuligowski and Halperin 1992). Cast iron cookware are excellent sources of iron (Kuligowski and Halperin 1992, Reilly 1985).

Very little information is available, however, on the mineral supplementation rates of stone cookware, used by early human populations. In California along the eastern foothill portion of the San Joaquin Valley, there are bedrock outcrops often used by early native Californians as bedrock mortars for pounding acorns into meal (Latta 1999). Most Sierran granitic rocks are not rich enough in potassium to be called granite (Hill 1975). They contain a high amounts of sodium- and calcium-rich feldspar and fall into the granodiorite or quartz monzonite groups (Hill 1975). Importantly, feldspar is a group of abundant rock-forming minerals occurring principally in igneous rocks, and consist of silicates of aluminum with potassium, sodium, and calcium. When these bedrock mortars are used in food preparation, portions of the rock are ground to powder form and incorporated into the food item. As a result, native peoples can acquire sodium and calcium mineral supplements from these bedrock mortars because of the presence of the feldspar mineral. These pulverized feldspars may react similarly inside the human body as clays.

A host of questions need to be answered. Did native groups of people realize that their stone cookware benefited them in terms of mineral supplementation? Were certain types of stoneware purposely selected for their mineral properties? Did native peoples trade stoneware pieces with other groups, so beneficial rock sources traveled to other nearby Indian communities? These and other questions should be addressed before the information is lost forever.

Literature Cited

Boyages, E. C. 1993. Clinical review 49. Iodine deficiency disorders. Journal of Clinical Endocrinology and Metabolism 77:587.

Davidsson, L. 1999. Are vegetarians an "at risk group" for iodine deficiency? British Journal of Nutrition 81:3-4.

Delange, F. 1998. Risks and benefits of iodine supplementation. Lancet 351:923-924.

Diamond, J. 1999. Dirty eating for healthy living. Nature 400:120-121.

Hill, M. 1975. Geology of the Sierra Nevada. University of California Press, Berkeley, California, USA.

Johns, T. and Duquette, M., 1991. Detoxification and mineral supplementation as functions of geophagy. Am. J. Clin. Nutr. 53:448-456.

Kreulen, D. A. and Jagger, T. 1984. The significance of soil ingestion in the utilization of arid rangelands by large herbivores with special reference to natural licks on the Kalahari pans. In: Herbivore Nutrition in the Tropics and Subtropics. Eds: Gilchrist, F.M.C. & Mackie, R.I. The Science Press, Craighall, South Africa. pp. 204-221.

Kuligowski J. and Halperin K. M. 1992. Stainless steel cookware as a significant source of nickel, chromium, and iron. Archives of Environmental Contamination & Toxicology 23:211-215.

Latta, F. F. 1999. Handbook of Yokuts Indians. Brewer’s Historical Press, Exeter, California, USA.

Marieb, E. N. 1998. Human Anatomy and Physiology. Fourth edition. Benjamin Cummings Science Publishing Co. Inc., Menlo Park, California, USA. 1192 pp.

Reid, R.M. 1992. Cultural and medical perspectives on geophagy. Med. Anthropol. 13:337-351.

Reilly C. 1985. The dietary significance of adventitious iron, zinc, copper and lead in domestically prepared food. Food Additives & Contaminants. 2:209-215.

Wiley, A. S., and S. H. Katz. 1998. Geophagy in pregnancy: A test of a hypothesis. Current Anthropology 39:532-545.