Concrete is often used to take the place of stone. Most people who visit an amusement park have no idea that most of what they see, no matter how natural looking, is concrete. Huge marble building faces - most often are concrete. I once lived in a home where a company built a hot tub from concrete which was as if carved from a boulder. It was more realistic than the real rock around it.
In these applications concrete is a practical way to duplicate nature - much more practical than finding, transporting and placing huge stones.
When Liquid Quarry makes a surround for a fireplace, a kitchen or bathroom counter, or a custom sink, we do not try to make it look like stone. Why? Although we disagree with the non sustainable practice of using real stone, it is much more practical than trying to imitate nature with concrete. Instead of taking advantage of the plastic ability of concrete to take on any shape, almost any colour or texture, we have been asked to make concrete appear to be marble. Why wouldn't we? Because it would be more cost effective to use marble. If our customer were looking for a green alternative first and foremost, we would likely do it!