[Solved] In horizontal analysis, if an item has a negative amount in the base year and a positive amount in the following year, no percentage change for that item can be computed. Calcium Carbonate: A chemical compound with the formula CaCO3, found in rocks such as limestone, chalk, and marble, and is the main component of shells of marine organisms. Chalk Formation: A type of limestone characterized by its fine, white, porous structure, formed from the accumulation of microorganisms' calcite shells. Microscopic Organisms: Tiny life forms, not visible to the naked eye, including bacteria, protozoa, and certain types of fungi and algae. Calcium Carbonate: A chemical compound with the formula CaCO3, found in rocks such as limestone, chalk, and marble, and is a major component of shells of marine organisms, snails, and eggs.