Some products that use limestone are not that obvious.

Adding Nutrients (click here) High quality limestone, such as found in California, is a source of calcium in foods and vitamins. Foods where limestone adds calcium include breads, granola bars, cereal, infant formula, pasta, pet food, tofu, yogurt, graham crackers, baking mixes, waffles...the uses grow daily. It also has many uses in making antacids and medicine tablets.