What Are Rubies Made Of? Unveiling the Secrets of the King of Gems

At its heart, a ruby is made of aluminum oxide (Al2O3), the very same substance that comprises the mineral corundum. What distinguishes a ruby from other forms of corundum, like sapphire, is the presence of chromium as a trace element. It is this chromium impurity that imbues the ruby with its characteristic and highly prized red color. The interplay of light and this specific atomic structure is what transforms ordinary corundum into the fiery gem we know and love as the ruby.

The Geochemical Cocktail: How Rubies Form

The formation of rubies is a rare and complex geological event, demanding a precise blend of ingredients and conditions. It’s not just about having aluminum and oxygen readily available; the presence of chromium, the absence of silica, and the right amount of heat and pressure are all critical.

From Magma to Metamorphism: The Birth of a Ruby

Most rubies are born deep within the Earth’s crust, in environments associated with either metamorphic or igneous rock formations.

• Metamorphic Rubies: These rubies typically form where aluminum-rich rocks like bauxite are subjected to intense heat and pressure during tectonic events like mountain building. The heat and pressure cause the bauxite to recrystallize, forming corundum crystals. If chromium is present in the surrounding environment, it gets incorporated into the corundum structure, giving rise to rubies. Many of the most famous ruby deposits, including those in Myanmar (Burma) and Mozambique, are associated with metamorphic rocks.
• Igneous Rubies: In rarer cases, rubies can form in igneous environments, specifically in magmatic rocks like basalts or syenites. As magma cools, elements crystallize out, forming various minerals. If the magma is rich in aluminum and contains chromium, rubies can form. However, the presence of silica is often a hindrance, as silica tends to form other minerals before corundum can crystallize. Consequently, rubies from igneous sources are generally smaller and less common than those from metamorphic environments.

The Role of Chromium: The Color Catalyst

Chromium is the key to a ruby’s color. When chromium atoms replace some of the aluminum atoms in the corundum crystal lattice, they absorb certain wavelengths of light. Specifically, they absorb blue and yellow light, while transmitting red light. This selective absorption is what gives rubies their characteristic red hue. The amount of chromium present determines the intensity of the red color. Too little chromium, and the corundum will be pink; too much, and the crystal will be opaque and unsuitable for gem use. The most desirable rubies have a vivid, intense red color, often referred to as “pigeon’s blood red”.

The Importance of Silica Absence: A Crucial Factor

The absence of silica (SiO2) is crucial for ruby formation. Silica is a common element in the Earth’s crust, and it readily combines with aluminum to form silicate minerals like feldspar and mica. If silica is present in abundance during corundum formation, it will outcompete oxygen for the aluminum, preventing the formation of aluminum oxide (corundum). Therefore, rubies are more likely to form in geological environments that are relatively depleted in silica.

Beyond the Basics: Exploring Ruby Varieties

While the basic composition of a ruby remains consistent (aluminum oxide with chromium), variations in color, clarity, and inclusions can lead to different ruby varieties. Some noteworthy examples include:

• Star Rubies: These rubies exhibit a phenomenon called asterism, a star-like effect caused by microscopic inclusions of rutile (titanium dioxide) aligned in specific directions within the crystal. When light shines on a star ruby, it creates a six-rayed star on the surface.
• Pigeon’s Blood Rubies: As mentioned earlier, this term refers to rubies with a very specific and highly desirable red color – a deep, vivid red with a slight hint of purple or pink. Pigeon’s blood rubies are often associated with Myanmar (Burma) and are considered to be among the most valuable rubies in the world.
• Burmese Rubies: Rubies from Myanmar (Burma) have historically been highly prized due to their exceptional color and clarity. While the term “Burmese ruby” is often used to refer to rubies of high quality, it technically only applies to rubies that originate from Myanmar.

FAQs: Decoding the Mysteries of Rubies

1. What is the chemical formula of a ruby? The chemical formula of a ruby is Al2O3:Cr, indicating that it’s primarily aluminum oxide (Al2O3) with chromium (Cr) as a trace element.

2. Is ruby harder than diamond? No, a diamond is harder than a ruby. Diamonds have a Mohs hardness of 10, while rubies have a Mohs hardness of 9. While a ruby is very durable, it can still be scratched by a diamond.

3. Can rubies be created in a lab? Yes, synthetic rubies can be created in a lab using various methods, such as the Verneuil process, the Czochralski process, and the flux growth process. These lab-grown rubies have the same chemical composition and physical properties as natural rubies.

4. How can I tell if a ruby is real or fake? Several tests can help determine the authenticity of a ruby. Observing the ruby under magnification to look for inclusions, checking its hardness, and using a gemological refractometer to measure its refractive index are all common methods. A gemologist can provide a definitive identification.

5. What are the most important factors that determine the value of a ruby? The primary factors that influence a ruby’s value are color, clarity, cut, and carat weight. The intensity and saturation of the red color are particularly important.

6. Do all rubies come from Myanmar (Burma)? No, rubies are found in various locations around the world, including Mozambique, Thailand, Sri Lanka, Vietnam, and Tanzania. While Burmese rubies are highly regarded, excellent-quality rubies are also found in other countries.

7. What is the difference between a ruby and a pink sapphire? The difference between a ruby and a pink sapphire is primarily based on the intensity of the red color. Generally, if the corundum has a strong, vibrant red color, it’s classified as a ruby. If the color is a lighter shade of pink, it’s considered a pink sapphire. However, the boundary between the two can be subjective and depends on the gemological laboratory’s grading standards.

8. Are rubies radioactive? No, rubies are not radioactive. The elements that make up a ruby, aluminum, oxygen, and chromium, are not radioactive isotopes.

9. What kind of inclusions are commonly found in rubies? Common inclusions found in rubies include rutile needles, zircons, crystals of other minerals, and fluid inclusions (small pockets of liquid or gas trapped within the crystal). These inclusions can sometimes help determine the origin of the ruby.

10. How should I care for my ruby jewelry? Rubies are relatively durable but should still be handled with care. Clean your ruby jewelry with warm, soapy water and a soft brush. Avoid exposing your rubies to harsh chemicals or extreme temperatures.

11. Can heat treatment affect the color of a ruby? Yes, heat treatment is a common practice used to enhance the color and clarity of rubies. Heat treatment can improve the red color and remove undesirable inclusions. However, it’s important to disclose whether a ruby has been heat-treated.

12. What is the symbolic meaning of rubies? Rubies have been associated with various symbolic meanings throughout history, including passion, love, courage, and prosperity. They are often considered symbols of royalty and power.