Marble forms when limestone or dolostone is subjected to intense heat and pressure within the Earth's crust, causing the original carbonate grains to recrystallize into an interlocking mosaic. The process destroys any original sedimentary structures or fossils. Pure marble is white, but impurities like clay, silt, or iron oxides create the characteristic veins and swirls prized in dimensional stone quarrying.
Heard on the job
The drill core shows a sharp contact between the schist and the marble unit.