Marble is a plentiful natural resource, but it is not a renewable resource. Marble is produced through the metamorphic process. It began its existence as limestone then was changed through exposure to heat and pressure over thousands of years. While their is an abundance of marble available to be quarried from regions around the globe, there is no way to create more.
The primary mineral in marble is still limestone, which is quite sensitive to common household acids, such as vinegar and citric acid. Some of these acids are present in bathroom cleaning products. Prolonged exposure to these acids can permanently etch marble.
Marble in a shower can become dull and unattractive if not properly and routinely maintained. You will need to clean your marble shower after each use. The Marble Institute of America recommends using a squeegee after each shower to help remove water and soap residue. Regular cleaning with a non-acidic bathroom cleaner, such as 1/2 cup of ammonia mixed with one gallon of water, can help prevent soap scum buildup.
If you love the warmth and elegance of a marble shower, but don't want the additional maintenance that goes with it, you might consider using cultured marble instead of natural marble. Cultured marble is a man-made material that blends crushed limestone with fiberglass resin to create a moldable material that mimics the look of natural marble. Cultured marble is usually finished with a tough, clear gelcoat that is non-porous, tough, stain-resistant and much easier to maintain than natural marble.