Marble is a result of a re-crystallization process that altered a limestone into a new variety of natural stone.  Limestone underwent further heating and applied pressure, and other elements such as fossil material and other minerals combined to form a new rock which we call marble.  The random mixture of elements account for the color variations and patterns that we see in various degrees in each marble slab or tile. 

These variations give marble great potential for decorative use.  Muted colors serve for subtle shading in interiors, while other varities of marble that come in more vibrant colors serve as bold accents.