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Iodine in Rocks
The medical research council has published an important review of the existing information on iodine in nutrition by Drs. John B. Orr and Isabella Leitch from the Rowett Institute, Aberdeen. Iodine is widely distributed but is present in inorganic and organic substances in small quantities. Hence the unit used for reckoning is one-millionth gram, for which the symbol γ is used. Excepting gneiss granite with 810 γ per kilogram, the amount in igneous rocks varies between 200 and 450 γ. Among sedimentary rocks, quartzites vary from 1,100 to 8,850, while gypsum, limestones and dolomites vary from 250 to 440. All arable soils contain iodine in quantities varying from 600 to 6,000 γ per kilogram. Plants have a great power of concentrating iodine, which is adsorbed by the resulting humus. This therefore has a higher content than the rocks from which it is derived. But iodine tends to
LONDON. JAMA. 1930;95(4):276-277. doi:10.1001/jama.1930.02720040034017