Many people refer to marble as a "soft stone," but what they really mean is that it reacts to acids. Simply said, most marbles etch when they come into touch with acids, ammonia, and alcohol (etch marks look as if the shine or the finish of the stone has been removed). This means that marble is not a good material for walls with acidic substances such as urine, vinegar, and fruit juice. However, if you want to use marble for something non-acidic, it can be cleaned with soap and water. There are two types of marble: soft and hard. Soft marble is used for countertops and other surfaces where great beauty is not important. Hard marble is more durable and can only be used for decorative purposes. The term "marble" actually refers to any variety of limestone. There are many different colors and patterns within this one rock type! The color of marble varies depending on how the stone was formed. Black marble results from the presence of fossilized plants and trees, while red and white marbles show up these colors due to the presence of iron oxide. Grayish-blue marbles have aluminum added during their production process, which gives them their unique color. Marble is a common material in building construction because of its beautiful appearance and acid-resistance properties. However, marble is very porous and should never be used as a flooring option.