The strength of marble comes from the transformation of its parent, limestone.
Metamorphic rock refers to a type of igneous or sedimentary rock that has been deformed and transformed. Through extreme geologic conditions, the stone actually changes on a molecular level. Common types of metamorphic rock include shale, slate, schist, marble and quartzite. All these stones came from a parent stone that was exposed to heat, pressure or a combination of the two.
When rocks are placed under conditions high in heat and pressure, they change or go through a metamorphism. During this process the stones are compacted and recrystalized. No chemical change actually occurs, but as the crystals regrow they organize themselves in different ways, creating a new stone. The crystals are forced to become stronger and more compact under intense heat and pressure. The stones are different in texture, grain size and strength after recrystalization.
Beneath landscapes of high geothermal activity are common areas where metamorphism occurs.
Dynamic metamorphism is a type of change that occurs as a direct result of a rock yielding to pressure. The pressure comes from layers of rock and sediment piling on top of it. There is little heat in this transformation; instead, the stone just bends or breaks beneath the weight or between colliding land masses along a fault line. According to the California Polytechnic University, these types of metamorphic rock contain grains of the original stone in a deformed matrix of rock.
This type of metamorphism occurs as a molten intrusion of igneous magma comes into contact with cool rock. It happens only along the line of contact between the magma and cool rock, called the metamorphic aureole. All the rock farther from that area is not affected. Heat and circulating fluids are the most important factors in this type of metamorphism. Typical temperatures are between 572 and 1,472 degrees Fahrenheit, according to the California Polytechnic University. Hornfels are stones formed by contact metamorphism.
Regional metamorphism occurs over large land areas, such as throughout entire mountain ranges. Increased geothermal temperature and pressure are the important factors in this type of metamorphism. Like dynamic metamorphism but with the addition of heat, the rock folds, creating a foliated pattern as seen in stone gneiss. Beneath landmasses like mountain ranges, rock is forced downward, and at greater depths there is more heat and pressure.