OK, this may be something you already know. And then again, it might not be. But contrary to what some people think, cement and concrete are not the same thing. Cement is a material used to make concrete. In a broader sense, cement is a general name for something that binds things together. So is glue. But the cement used in concrete is a hydraulic cement or one that hardens with the addition of water. It's usually called "Portland Cement". It was patented in 1824. Concrete is made up of three basic ingredients: an aggregate (rock, sand, or gravel) water, and of course, the Portland cement. We all think of concrete as being a dull, and uninteresting gray mass, of hardened structural material. But you might be pleasantly surprised if you could see the aggregate in the hardened concrete. Grinding and polishing a concrete floor can expose the aggregate. And depending on the aggregates used in the concrete mix, grinding and polishing the floor can expose beautiful colors in the stones. Further polishing the floor with finer and finer diamond grinding can produce beautiful colors and a marble-like shine.