How is marble formed?

Marble is formed when limestone or dolomite (rocks composed of calcium magnesium carbonate) recrystallizes under the influence of intense heat, pressure, and chemical changes involving aqueous solutions, a process called metamorphism. This recrystallization produces a denser rock and gives marble its distinctive crystalline structure.

Significant heat and pressure are required for the formation of marble. The pressure comes from the weight of overlying rocks, which can be thousands of meters thick, or from large-scale tectonic movements, while the heat is often provided by intrusions of magma onto cooler rock. Due to the combination of these factors, the calcite in limestone changes at the granular level, interlocking tightly to produce a solid and crystalline texture and transforming into marble..

During metamorphism, silicate minerals (silicon-oxygen compounds) in limestone can color the marble produced, while fine scales of graphite can result in gray or black streaks.