Limestone contains at least 50 percent calcium carbonate by weight. When placed in hydrochloric acid, limestone effervesces, or creates bubbles, due to the formation of carbon dioxide. Calcium carbonate is found in many consumer products such as antacid tablets and sidewalk chalk.
Limestone is a type of sedimentary rock that originates in bodies of water where shells and bones of dead marine organisms accumulate. Over millions of years, pressure compresses the sediment into rock. Due to the presence of limestone in Michigan, Indiana, and Illinois, scientists believe these areas were once underwater. Limestone was used by the ancient Egyptians to build pyramids.