Chalk is made up of a type of limestone, a compound made of Calcium and Oxygen. Chalk is formed by the shells of microscopic marine organisms, often containing
fossils from ancient seabeds.
Vinegar reacted with the Chalk to produce Carbon Dioxide gas, water and an aqueous compound.
2CH3CO2H(aq) + CaCO3(s) > 2Ca(CH3CO2)2(aq) + CO2(g) + H2O(l)
Limestone caves are formed when the limestone itself is dissolved by weak acids present in groundwater. This process occurs over many years and can eventually lead to forming massive formations as seen in the
Jenolan caves.
A similar process occurs when
acid rain touches marble statues... a major issue in historic areas.