Calcite vs Aragonite: What Are They, And What’s The Difference?

For nearly 100 years, scientists have been perplexed by a process that is critical to much of life in the world’s oceans.

That is why the solid calcium carbonate, originating in corals and seashells at times, emerges as calcite and sometimes as aragonite.

MIT scientists have discovered why and we share the discoveries of Calcite vs Aragonite, their similarities, differences, and how to differentiate them below.

What is Calcite?

Calcite is a Calcium Carbonate mineral that is white or has no color.

It is a key component of sedimentary rocks, including limestone, marble, and chalk.

It can be found in a crystalline configuration such as Iceland spar or deposited in caves as stalactites and stalagmites.

What is Aragonite?

Aragonite is a carbonate mineral, like calcite.

It is one of the three most prevalent crystal forms of Calcium Carbonate (CaCO3) found in to exist naturally—the additional configurations being the minerals Vaterite and Calcite.

Biological and physical activities, such as precipitation from marine and freshwater ecosystems, contribute to its formation.

Why do People Confuse Calcite and Aragonite?

Aragonite is a variant of calcite, which means it will have the same composition as calcite but a distinct structure, alignment, and crystal forms.

The ions from the carbonate are not in a solitary plane focusing on a similar path as they do in Calcite.

Scientists say that Aragonite is a chemically identical form of the mineral that is more soluble — and thus more vulnerable to ocean acidification.

What are the Similarities Between Calcite and Aragonite?

The number one similarity between Calcite and Aragonite is that they are both mineral features of Calcium Carbonate.

Calcite and Aragonite have the exact chemical formula, which is CACO3.

They are the two most prevalent phases of Calcium Carbonate.

Either Calcite or Aragonite creates the husks and skeletons of numerous marine life.

Both minerals can often be discovered in the same cave. 

What are the Differences Between Calcite and Aragonite?

When looking at Calcite vs Aragonite, Aragonite can be transformed to Calcite but not vice versa.

The structure of Calcite is referred to as trigonal, while the aragonite structure is described as being orthorhombic.

Researchers studying these materials have revealed that variations in the quantity of Magnesium in the water had previously been discovered as a significant role in the process of making Aragonite more soluble than Calcite. 

Still, researchers were consistently unable to explain the reason the Magnesium in the water had such a dramatic influence.

MIT Scientists in coalition with the National Laboratory at Lawrence Berkeley have now examined the mechanism at the atomic level. 

“The big-picture challenge is about materials formation…When solids crystallize in solution, stable crystal configuration with the lowest level of energy is expected.”

Numerous materials evolve better in a metastable state, meaning they are stable under typical situations but can change to a more stable condition eventually. 

Metastable forms, for example, are more soluble, and that’s advantageous for medications since it allows them to be more easily absorbed by the body. 

Different techs, like battery substances and water-separating photocatalysts, necessitate long-term stability and perform better in the stable stage.

Calcium carbonate can be found in two forms.

The stable form is Calcite, while the metastable form is Aragonite: It can eventually change into calcite over time or when heated. 

Diamond vs. graphite, which makes pencil lead, is another well-known illustration of such materials, as the researcher explains: Diamond, in this case, is the metastable configuration, and it will eventually convert to graphite, despite the fact that they both have the same composition – pure carbon.

Calcium carbonate generally crystallizes as calcite; however, in seawater, it crystallizes as aragonite.

The result has an impact on a variety of processes, including the global carbon cycle, which involves converting CO² in the environment into a strong mineral and restricting its accumulation in the atmosphere.

It also has an impact on the creation of corals and shells, whose aragonite crusts are susceptible to the acidity of the oceans brought on by climate change.

While scientists have known for a long time that variable quantities of magnesium in the surrounding water impact the destiny of calcium carbonate, they’ve never been able to explain why.

The MIT researchers discovered that the calcium-to-magnesium ratio in the water has an effect on the surface energy of nucleating crystals; once the ratio reaches a certain level, the balance shifts from calcite to aragonite formation.

The Researcher claims that exterior energy is the impediment to nucleation.

“We managed to compute the impact of magnesium on surface energy,” says the researcher. “We found that this was the means by which magnesium blocks the creation of the stable phase,” he adds, adding that while this surface energy is difficult to quantify experimentally, the team was able to identify it using atomic-level simulations.

A participant claims that if no magnesium is present in the solution, stable calcite forms soon. “However, as the magnesium concentration rises, the surface energy of calcite rises, and its nucleation rate falls based on magnitude,” he says. “Calcite nucleation eventually freezes out, and you’re left with the stage of metastable aragonite.”

The predicted outcomes almost match the percentages of the two configurations found experimentally when the magnesium ratios are altered, demonstrating that the technique may be used to forecast how other compounds would emerge from a solution, according to one scientist.

According to one MIT researcher, the team picked calcium carbonate to research metastability because it has decades of rich experimental data, making it a suitable case for investigating the reason for some chemical outcomes preferentially yielding one of the multiple potential forms a substance.

The ultimate goal of the MIT team is to forecast and control which materials form under diverse chemical conditions, allowing them to regulate the production of new materials with desirable properties such as clarity, chemical reactivity, hardness, or conductivity.

How to Locate Calcite and Aragonite

The two main places that these minerals are known to be situated are Caves and some seabeds.

In Slovakia, the Ochtinská Aragonite Cave is, as the name suggests, an Aragonite cave.

Carlsbad Caverns and other caves in the United States consist of Aragonite in stalactites and “cave flowers” (anthodite). 

On the ocean floor of the Bahamas, vast amounts of Aragonite sand can be located.

It is in the form of oolites, which are rock sediments constructed from ooids.

Finally, with the recent breakthrough by scientists, rock enthusiasts will get an even deeper understanding of the mysteries surrounding Calcite and Aragonite.

In the meantime, happy hunting and research.