Many cereals are full of important vitamins and "minerals." These minerals aren't minerals in the geological sense of the term. Remember that a mineral is a naturally occurring substance with a specific chemical composition and a definite crystalline structure that (usually) is not made by living things. The zinc in cereal comes from the mineral sphalerite. The calcium in cereal comes from the mineral calcite. And the iron in cereal comes from the mineral iron-stone. So although the food industry calls zinc, calcium, and iron, "minerals," they are not themselves minerals, but come from minerals.