Marble is a metamorphic rock. It was once limestone, but over time, the combination of intense heat and pressure, caused the limestone to re-crystallize. Foreign substances often entered the stone during this process, creating an infinite variety of colours, asters, and veining. Marble is a lot like snowflakes, no two pieces are exactly alike. Limestone is quite often referred to as marble. Marble is a sedimentary rock consisting of weathered and deposited limestone which has been mixed with calcite as a natural binder to form homogeneous material.