PrintWhen annealing flint, you can expect chalk or limestone to be present. Chalk and limestone are composed primarily of calcium carbonate (CaCO3), which is the same mineral present in hard water. It often shows up as a white residue on plumbing fixtures. If chalk or limestone is heated above 800° C (obtainable with charcoal), the gas carbon dioxide is released from the calcium carbonate leaving lime (CaO). Lime produced in this matter is referred to as quicklime or burnt lime. If water is added, this quicklime or burnt lime hydrates to form a white pasty substance known as slaked lime.
It is quite possible that an observant fire tender or cook could have noticed that, after encountering rain, this material would dry and form a hard substance. We refer to the substance as lime mortar, a type of cement. It is common to confuse the term cement with concrete. Cement is a binder or material that glues things together. Concrete, on the other hand, is a combination of cement and aggregate (sand, stone, etc.). Concrete is one example of a composite material. As we will see in this lesson a composite material is a material that is composed of two or more distinct materials in combination. Cement is the material within concrete that binds the stone and sand together.
In addition to the development of lime mortar in the Fertile Crescent, the Incas, and the Mayans independently discovered lime mortar around 5000 BCE, and it was widely used in ancient Rome and Greece around 4000 BCE.
