Georgia Marble

The land area known today as Georgia has been shaped by multiple continental collisions.  Hundreds of millions of years ago, a vast ocean separated 2 supercontinents–Laurentia and Gondwanaland.  Georgia was part of the former.  Volcanoes emerged in the fracture between the 2 continental plates, creating islands.  Some of these islands collided with Laurentia in the region that was to become Georgia.  This caused the uplifting of mountains as the islands pushed over the landmass of Laurentia.  The 2 supercontinents, influenced by the earth’s rotation, slid over the earth’s mantle and drifted toward each other.  First, the continental shelf of Gondwanaland struck Laurentia, then the 2 supercontinents themselves collided.  Both of these collisions caused the uplifting that birthed the Appalachian Mountains.  Later, the 2 supercontinents rifted apart and drifted in opposite directions, creating a massive rift valley that became the Atlantic Ocean.  In the process Gondwanaland left a piece of Africa behind in Georgia and South Carolina.

The continental collisions spurred much volcanic activity.  Volcanoes produce molten lava which when cooled becomes igneous rock.  Water erodes igneous rock into sediment that eventually can become cemented together into sedimentary rock.  Geological processes of subduction can cause both igneous and sedimentary rock to become buried deep underground where it is exposed to great pressure and heat, changing the rock’s composition or, in another word,  metamorphizing it, hence the name, metamorphic rock.  Metamorphic rock also erodes into sediment that can eventually become sedimentary rock.  This is known as the rock cycle.

Marble is a metamorphic rock that originated from living organisms.  Animals with shells made of calcium carbonate, such as clams and snails, first evolved about 500 million years ago.  Shells of countless numbers of these organisms became buried and cemented together to form limestone.  Limestone subducted deep underground becomes exposed to high pressure and heat, changing its composition to marble.  Millions of years later uplifting and erosion expose these marble veins to the surface.  Georgia has some of the best marble in the world.

Map of the Murphy Marble Belt in Georgia.  The red lines indicate where the marble outcrops.  Marble is relatively rare on earth because it couldn’t have become metamorphized limestone until after organisms with shells evolved.

The Tate House made of pink Etowah marble.  Sam Tate consolidated the Georgia Marble industry early during the 20th century and had this mansion built for fancy living.  No paint was necessary to give the house this color.  It’s located near Nelson, Georgia where there is a schoolhouse made from marble and a marble museum.

The area where marble outcrops in Georgia is known as the Murphy Marble Belt.  The Cherokee Indians made use of marble, but Europeans forced them off the land and established the marble industry.  (Historical footnote:  the Supreme Court ruled in favor of the Cherokee Indians, but the U.S. government ignored the Supreme Court ruling and forced them to leave the state anyway, leading to the infamous and tragic Trail of Tears.  President Andrew Jackson hated Indians.)  Marble is resistant to water erosion, yet is soft and easy to carve, making it ideal for building materials and for sculpturing statues.

There are 3 types of marble in Georgia: Cherokee white, Etowah pink, and Creole gray and white.  The gray in the latter is an impurity of clay that mixed with the limestone before it became metamorphized.

The Murphy Marble Belt in eastern Georgia consists of 3 kinds of metamorphic rock–quartzite, limonite iron ore, and marble.  This apparently corresponds to geological strata in western Georgia that did not get subducted and metamorphized and instead consists of 3 sedimentary equivalents–sandstone, iron ore, and dolostone (a type of limestone).

Reference:

Gore, Pamela; and William Witherspoon

Roadside Geology of Georgia

Mountain Press Publishing 2013

Advertisement

Tags: continental drift, marble, metamorphic rock, the rock cycle