Traditional pool plaster surfaces are composed of cement and crushed marble fines.  They are smooth by nature and many colors are available through the addition of color pigments.  A pebble type pool finish is an exposed aggregate, meaning there are small rocks embedded in the finish.  Whereas, they provide a beautiful look they tend to be rougher on the feet than a traditional plaster.  The longevity of both of these finishes rest solely on proper water chemistry and can easily last up to 20 years.