What is Dolomitization? - Formation, Origin & Formula

Instructor: Betsy Chesnutt

Betsy teaches college physics, biology, and engineering and has a Ph.D. in Biomedical Engineering

What is dolomitization and how does it happen? In this lesson, you'll learn about the process of dolomitization, including how it's formed, its origins, and much more.

What is Dolomite?

In northern Italy, tall mountains made of a peculiar white stone grace the landscape. These mountains are primarily made of a very interesting type of stone. It looks like limestone, but there are some important differences.

In 1791, a French explorer collected some samples of this mysterious white rock and conducted experiments to find out exactly what it was. When limestone is exposed to acids, crystals of calcite and aragonite inside the limestone react very strongly. However, when these white rocks were put in contact with acids, nothing happened. He wasn't sure exactly what kind of rocks these were, but it was clear that they weren't limestone.

Another scientist, Richard Kirman, first identified this mysterious rock as a new mineral called dolomite just three years later. The mountain range that had previously simply been called the Pale Mountains was renamed the Dolomites.

These white mountains in Italy are primarily made of the mineral dolomite.
A mountain in the Dolomites

How does Dolomite Form?

Even after the discovery of dolomite, for many years it was still unclear exactly how this rock had formed. Scientists noticed that there were a lot of marine fossils embedded in the Dolomite mountain range, so they surmised that it must have once been under the ocean. In fact, we now know that the land that would eventually turn into a series of imposing white mountains was once a very large coral reef.

The rocks that would one day become the Dolomite Mountains were changed from limestone to dolomite when they were underwater as part of a coral reef like the one that forms this atoll.
coral reef atoll

While the land was still under the sea, the original limestone, which contained a lot of calcium carbonate (CaCO3) crystals, was repeatedly infused with magnesium-rich water. This happened many times over a very long time period until most of the calcium carbonate crystals were replaced with calcium and magnesium carbonate (CaMg(CO3)2) crystals, which make up the mineral we now know as dolomite. The process in which dolomite is produced from limestone is called dolomitization.

The Characteristics of Dolomite

Although the mineral dolomite was first identified in the mountains of northern Italy, it is found in many locations throughout the world. Sometimes dolomite occurs on its own, but often it is found mixed in with limestone. In fact, it's also common to find rocks that contain both the calcium carbonate that is characteristic of limestone and the calcium and magnesium carbonate that is characteristic of dolomite. This is known as dolomitic limestone.

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