How Do Gemstones Form? A Deep Dive Into The Earth’s Magical Crevices

Gemstones have been the object of affection for civilizations for thousands of years. Cleopatra adorned herself in veils of precious gemstones including emeralds and carnelian. The ancient Egyptian queen wasn’t the only member of royalty to don glittering gems. Presently, the Duchess of Cambridge, Kate Middleton, frequently flaunts rare jewels, including diamond tiaras and tanzanite earrings. Pirates navigated the seven seas in their quest for hidden treasure. It’s no secret society loves them, but how do gemstones form?

From the azure-hued lapis-lazuli to diamonds galore, these brilliant treasures from nature undergo a long process before decorating the necks of royalty and fingers of brides-to-be. Let’s dive into the earth’s crust to discover the intricate process of gemstone formation!

What Are Gemstones?

Before we examine the (arti)facts of how gemstones form, we should probably know exactly what we’re working with, right? In other words, what are gemstones?

Defining these jewels is complex because there are hundreds of specimens considered to be gemstones. In the simplest terms possible, gemstones are defined by the Gem Society as:

“Minerals that have been chosen for their beauty and durability, and then cut and polished for use as human adornment.”

As straightforward as this definition is, there are cracks in it. That’s mostly because gemstones aren’t always decorative, and there are two types of gemstones: minerals and organics. Minerals are created within the earth, whereas organics are live organisms such as pearls and amber. With this in mind, let’s get back to the question at hand…

How do gemstones form

How Do Gemstones Form?

Gemstones form over thousands of years in the layers of the earth’s crust. In order to grow, gemstones require five criteria:

  1. Minerals, and/or mineral ingredients
  2. Temperature
  3. Pressure
  4. Time
  5. Space

When these five criteria work together, a magical process of mineral crystallization occurs. The result? The growth of hardened, crystallized minerals known as gemstones!

While the process is much more dynamic than the simplified explanation above, you can see a real-life example in the form of rock candy! If you stir a sizeable lump of sugar in water, the sugar will ultimately settle to the bottom. When that happens, the sugar has reached a saturation point. From there, boiling the water and adding more sugar will reach a boiling point. After that, removing the boiling water from heat will cause excess sugar to crystallize. If you hang the sugar on a string the result is crystallized hard candy!

The process isn’t much different for gemstones to grow in the earth. However, instead of forming in a pot with boiling water, gemstones fall into four categories of formation.

how do gemstones form

The Four Processes of Gemstone Formation

Nearly all gemstones form within the top layer of the Earth’s crust, which runs from 3-25 miles deep. However, there are outlier gemstones that grow in the mantle — diamonds, and peridot. Remember when we said there are hundreds of specimens that qualify as gemstones? Well, they grow in the three types of rock within the earth’s crust — igneous, sedimentary and metamorphic. 

Here’s a look at the four different gemstone formation processes:

Igneous Gemstone Formation

Precious gemstones including diamond, ruby, sapphire and peridot each form deep in the earth’s mantle where the temperature is extremely high. This geothermal layer is the prime ingredient to form sparkling diamonds. Up to 150-miles beneath the earth’s surface, gemstones like diamonds crystallize within the magma. Because the magma is fluid and incredibly hot, it rises with violent volcanic eruptions and breaks into dissolved rocks. 

Over time, these rocks emerge at an expedition rate to the surface. The diamonds rise so quickly that to the surface that they don’t have time to vaporize. The result is broken crystals under the weight of immense pressure. These crystals spill into the fractures of the crust and crystallize, which seals the fractures together. Then, volcanic eruptions force these crystallize formations to the surface, where miners excavate them to become gemstones!

how do gemstones form - igneous gemstone formation

Sedimentary Gemstone Formation

Sedimentary rock is a layer in the earth’s crust between igneous rock and metamorphic rock. Instead of rising from volcanic force to the surface, sedimentary gemstones form when rich mineral water seeps down into the cavities of the earth. That’s where mineral deposits form and gemstones like opal and azurite grow. With sedimentary rock, minerals blend with silica or other compounds and beautiful gemstones form. 

how od gemstones form - sedimentary gemstone formation

Hydrothermal Gemstone Formation

Remember how rock candies form? Well, hydrothermal gemstone formation is very similar. Highly saturated water filled with minerals gets pushed into the fractures and cracks in the earth’s crust. As the water cools, the minerals crystallize. 

You can thank this process for sparkling emeralds, which crystalize in hydrothermal deposits filled with chromium. In fact, chromium is the reason emeralds are strikingly green. One of the most popular hydrothermal mineral veins is the Muzo Emerald Mine in Colombia.

how do gemstones form - hydrothermal

Metamorphic Gemstone Formation

It’s phenomenal to think that a tiny little gemstone has undergone the collision of tectonic plates, but that’s exactly what happens with metamorphism. When tectonic plates move in the earth’s lithosphere (the crust and upper mantle), minerals conjoin under pressure and heat. Metamorphic gemstone formation occurs as a result of this collision. And that’s how beautiful gemstones like zircon and nephrite form!

How do gemstones form - metamorphic

A Final Note on Mineral Crystallization and Gemstone Formation

The process of gemstone formation is diverse and fascinating. It’s amazing to think that the sparkling jewels we know and love endured an extensive collision of elements and geology. While the four processes are individual, they share a commonality which answers the question, “how do gemstones form?” To summarize, gemstones form in the cracks deep within the earth’s crust. Within these tiny crevices, a force fusion of heat and pressure form a pressure cooker for gemstones. Over time, the crystal hardens and rises to the earth’s surface. From there, miners excavate the gemstones and sort them to be rough specimens or faceted gemstones. 

While the jumble of elements might seem offbeat or unpredictable, crystallization is a calculated technique only mother nature can produce. In that regard, gemstones truly are like blossoming seeds ready to bloom into beautiful gemstones!

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