What is Limestone?

Limestone is a sedimentary rock made mainly of calcium carbonate (CaCO₃), most commonly in the form of the mineral calcite. It often forms from the accumulation of shells, coral, and other marine material that settles on the seabed. Over millions of years, these layers are compacted and hardened into limestone.

Its wide range of uses and its natural availability make limestone one of the most important raw materials used by societies around the world.

Key Characteristics:

Colour: Limestone can be white, beige, grey, or even bluish. The colour depends largely on impurities such as clay, sand, iron compounds, or organic material mixed into the stone.

Texture: It is usually fine-grained, but the texture can vary quite a bit. Some limestones are smooth and dense, while others are rough and porous, especially if they contain fossil fragments or have been weathered.

Hardness: Limestone is relatively soft compared to many other rocks. This makes it easy to cut, shape, and process, which is one reason it has been widely used in construction for centuries.

Reaction with Acid: One of limestone’s defining characteristics is its reaction with acids. When a weak acid such as vinegar or lemon juice is dropped onto limestone, it will fizz as carbon dioxide gas is released. The fizzing is most obvious when the limestone contains a high proportion of calcite and the surface is fresh. On very dense or weathered surfaces, the reaction can be slower or subtler.