Mineral of the Month: Aragonite

Welcome to our 'Mineral of the Month' series, where we embark on a journey through the world of minerals, one radiant rock at a time. Each month, we'll shine a spotlight on a unique and fascinating mineral, unveiling its geological secrets and the stunning beauty that lies within. Whether you're a seasoned mineral enthusiast or just beginning to explore the wonders of the Earth's treasures - both fluorescent and not, our series promises to ignite your curiosity and leave you with a newfound appreciation for the minerals that adorn our planet.

As your trusted source for fluorescent minerals, we've chosen aragonite as the current "Mineral of the Month" to share with you.

Imagine a mineral that glows in a rainbow of colors under ultraviolet light—a true testament to the beauty that nature conceals beneath the surface. In this blog post, we'll take you through aragonite's formation, its history and how it takes pride in our fluorescent mineral collections all over the world.

Aragonite Chemical Composition and Crystal Structure

At its core, aragonite is a calcium carbonate mineral. In chemical terms, its formula is CaCO3, which means it's composed of calcium (Ca), carbon (C), and oxygen (O) atoms. While calcium carbonate is a common mineral, what sets Aragonite apart is its unique crystal structure.

Aragonite belongs to the orthorhombic crystal system, a geometric arrangement that results in distinct, needle-like crystals. Unlike its close relative, calcite, which forms rhombohedral crystals, aragonite's needle-like structures give it a special allure. These crystals often grow in radiating clusters or delicate spires, creating quite the visual spectacle.

Aragonite Historical Significance

The story of aragonite begins in the late 18th century when it was first discovered and formally recognized as a distinct mineral species. The credit for this goes to the Spanish mineralogist Abraham Gottlob Werner, who bestowed upon it the name "aragonite" in honor of the region of Aragon in Spain, where it was initially found. Since its discovery, aragonite has garnered immense attention from scientists, mineral collectors, and historians alike.

Beyond its naming, aragonite holds historical significance in various fields. It has played a pivotal role in geology, as its formation processes shed light on the Earth's geological history. Additionally, its presence in fossils, particularly in the shells of marine organisms, has provided valuable insights into the world's prehistoric oceans and the creatures that inhabited them.

As we talk more about aragonite, you'll discover how this mineral has left a mark in the world of science, art, and culture.

Aragonite Geological Formation and Occurrence:

Aragonite, like its close cousin calcite, originates primarily from the precipitation of calcium carbonate from aqueous solutions. However, what sets aragonite apart is the specific conditions under which it forms.

Marine Environments: Aragonite is commonly found in marine environments, especially in shallow, warm waters. The photo above shows a piece of aragonite formed on the sea floor from the compression of small skeletons and shells of living creatures. Shown under shortwave UV light. Found in Malaea, Maui, Hawaii, USA back in 2013. Photo courtesy of Fluorescent Minerals Workgroup MKA. 

Here's how it happens:

Biological Activity: Marine organisms, such as corals, clams, and some types of algae, play a pivotal role. They extract calcium ions and bicarbonate ions from the surrounding seawater to build their shells and skeletons. These ions react to form calcium carbonate, which, under the right conditions, crystallizes into aragonite.

Supersaturation: Aragonite forms when the water is supersaturated with calcium carbonate. This occurs when factors like increased temperature, pressure, or a decrease in carbon dioxide levels cause the water to become oversaturated with respect to calcium carbonate.

Microbial Activity: Microbes can also influence the formation of aragonite in certain environments, adding another layer of complexity to its genesis.

Speleogenesis: In caves, aragonite can form as a result of the slow deposition of calcium carbonate from dripping water. Stalactites, stalagmites, and other cave formations often contain aragonite. 

Lead-bearing aragonite: from mindat.org, “Traditionally called 'tarnowitzite', much 'tarnowitzite' has been identified as a mixture of aragonite and cerussite, but lead-bearing aragonite with up to 3% PbCO3 may be homogeneous.” 

Aragonite Physical Properties

Color:

Aragonite presents a wide array of colors, ranging from colorless to white, but it's also known to showcase various shades of yellow, orange, brown, blue, and green. The spectrum of colors can be influenced by impurities, inclusions, and environmental factors during its formation.

Luster: 

Aragonite exhibits a vitreous to resinous luster, depending on the specific specimen. This luster gives it a distinctive shine and a glassy appearance that catches the light in a captivating manner.

Hardness:

On the Mohs scale of mineral hardness, Aragonite scores a 3.5 to 4. This means it is relatively soft compared to some other minerals, which makes it susceptible to scratching. While its softness can pose a challenge for collectors in terms of preservation, it also means that aragonite can be beautifully polished to enhance its natural luster and color.

Fluorescence:

The crown jewel of aragonite's physical properties is undoubtedly its fluorescence and phosphorescence. You can read more about phosphorescence here. Aragonite often exhibits a remarkable response to ultraviolet (UV) light. When exposed to UV light sources, such as 255nm shortwave UV light, aragonite can emit a stunning and mesmerizing glow. The colors it fluoresces in can vary, including shades of blue, green, yellow, and pink, depending on the impurities present in the mineral.

This unique fluorescence property has made aragonite a sought-after glow rock among mineral collectors and enthusiasts.

Where can I find fluorescent aragonite?

Collecting fluorescent aragonite can be a rewarding pursuit for mineral enthusiasts, but it's important to know where to look for specimens that exhibit this unique property. While aragonite is found in various locations worldwide, not all of them produce fluorescent specimens. Here are some places (natural and not) known for yielding fluorescent aragonite:

Aragonite from Mexico

Mexico: Several caves and underground systems in Mexico are home to fluorescent aragonite formations. Notable locations include the Santa Eulalia Mining District in Chihuahua, producing quality aragonite specimens. These crystals often fluoresce brilliantly under UV light and are phosphorescent as well.

Italian Aragonite, Photo Courtesy of Chris Clemens

Italy: Italian caves and mines such as the sulfur mines of the Agrigento region of Sicily, are known for their aragonite specimens with incredible fluorescence. These Italian aragonites are also famous for their longlasting phosphorescence.

United States: Aragonite is found throughout the United States in areas such as Utah, Wyoming, Montana, Arizona, New Mexico and more.

Online and Mineral Shows: In addition to collecting in the field, mineral enthusiasts can also find fluorescent aragonite specimens through reputable mineral dealers, both online and at mineral shows. Many collectors and dealers offer a wide range of specimens, including aragonite.

Cave Tours and Guided Excursions: Some caves and underground formations that contain fluorescent aragonite are accessible through guided tours and excursions. These tours provide a safe and educational way to explore these unique geological wonders and may even allow you to acquire specimens.

Natural History Museums: While not for collecting, visiting natural history museums with mineral exhibits can provide an opportunity to view and appreciate fluorescent aragonite specimens. These displays can offer valuable insights into the mineral's beauty and fluorescence.

Before embarking on any collecting expedition, it's essential to obtain the necessary permits, follow ethical collecting practices, and prioritize safety. Additionally, be aware of legal regulations regarding mineral collecting in specific locations, as collecting may be restricted or prohibited in certain areas to protect natural resources and cave ecosystems.

Fun Facts and Trivia

Here are some fun facts and trivia tidbits about aragonite:

Stalactites and Stalagmites: Aragonite plays a significant role in the formation of these cave features. Its needle-like crystals slowly grow over time as mineral-rich water drips from the cave ceiling, creating spectacular underground landscapes.

Collectible Radiance: Aragonite's fluorescence makes it a highly sought-after mineral among collectors of fluorescent specimens. Its ability to emit a vibrant glow under ultraviolet light adds a whole new dimension to mineral appreciation.

Historical Significance in Art: Aragonite has been used as a carving and decorative stone in various cultures throughout history. Its lustrous appearance and ease of shaping have made it a popular choice for sculptures, cameos, and ornamental objects.

Coral Reef Builder: In marine ecosystems, corals use aragonite to build their intricate skeletons. The health of coral reefs is closely tied to the availability of aragonite in seawater, making it essential for the vitality of these underwater wonders.

In closing, we hope you've enjoyed our exploration of Aragonite, our 'Mineral of the Month,'. Join us next month as we continue to unearth the hidden gems of our world, one mineral at a time. Stay curious, keep collecting, and let the beauty of minerals continue to inspire your sense of awe and discovery.