I Didn’t Know That. . .

Q: What rock is a food?

A: Although trace metals isolated from minerals are a necessary part of our diet, only one rock is used directly as a food--sodium chloride, or rock salt. Thick beds of salt underlie certain areas of the Earth’s surface, said geologist Richard M. Pearl, and seepages bring salt to the surface in the form of salt licks and salt springs. The location of available salt has controlled caravan routes and the siting of settlements in many countries. The isolation of salt from the ocean and other sources of saltwater was probably one of the first human industries, Pearl says.