Metamorphic stone results from layers of stone that were changed from their original state into a new type of stone due to heat, pressure, the introduction of other minerals, or combinations of heat, pressure, and chemical minerals.
Our best example of Metamorphic Stone in the state of Vermont is our lovely white marble. This marble started out as shells of ancient sea life. These creatures formed their protective shells from the calcium in the seawater. Countless trillions of these creatures lived and died to form thick layers on the ocean floor. Layers of calcium also precipitated naturally in some of the shallow ancient seas to form layers. In both events, these layers formed into limestone with the help of the metamorphic forces of heat and pressure.
Over long periods of time, these layers that were once under the sea at the edge of the continent came under great stress from compression due to the shift of the continental plates. The resulting heat and pressure was sufficient to soften and reform the limestone into marble. At this time, the limestone came into contact with other minerals in aqueous solution that intruded into the cracks and crevices. Depending on the exact chemical, these minerals added the wonderful black, gray, gold, and green veining we see in our white marble.