Most of what has been published about iodine in the environment has come from the studies of the consequence of human iodine deficiency referred to as endemic goiter. Goiter has almost disappeared with the recognition of the importance of dietary iodine and it's routine addition to table salt. Igneous rocks avg.
Sedimentary rocks avg.
Evaporative sodium chloride deposits are surprisingly depleted in iodine. A chemist unfamiliar with iodine would expect it's easy incorporation into the sodium chloride crystals due to the chemical compatibility of the two elements. However, the data does not support this assumption. The data reveals that sedimentary rocks are enhanced in iodine and that soils are concentrated even further. Some soils are amazingly enriched, large areas of Texas average 20,000 ppb soil iodine.