Backstory

This journey started with my desire to create a striking ring featuring a sizable ruby, not just for its aesthetic appeal but also as a thoughtful DIY gift.

The initial hurdle was acquiring a large ruby. Online gemstone retailers listed exorbitant prices, ranging from $2000 to $20,000 per carat (with one carat equaling 0.2 grams). Even the smallest natural rubies began at approximately $200, revealing that genuine rubies were far more costly than I had anticipated.

Desperate for a more budget-friendly option, I turned to eBay, where I discovered numerous listings for rubies priced at around $0.50 per carat. I found a well-cut 10-carat ruby for just $20 and made the purchase.

Seeds of Doubt

Upon its arrival, the ruby dazzled with its deep red color and substantial size, leaving me in awe of its beauty. However, when I shared my find with a friend, his reaction was less enthusiastic. He posed skeptical questions regarding its cost and authenticity, prompting me to consider whether I had been duped.

Trust, but Verify

In essence, the authenticity of my ruby was not paramount—it looked stunning regardless of its true nature. However, the experience highlighted how little we often know about various aspects of our lives. In a world filled with complexities, we trust that businesses and regulations provide us with accurate information, yet we often remain in the dark.

Determined to uncover the truth about my ruby's composition, I decided to conduct some tests.

Ruling Out Stones

To provide context, rubies are crystalline structures with the chemical formula Al?O? and a density ranging from 3.98 to 4.02 g/cm³. Composed of corundum, they derive their striking red color from trace amounts of chromium.

Various red gemstones exist that can mimic rubies, each with distinct chemical properties and hardness levels. After extensive research, I devised several at-home tests to differentiate my ruby from its imposters.

Here’s a random image of a red gemstone for you to ponder its identity.

The primary ruby substitutes, ranked by value, are: 1. Natural Ruby 2. Red Spinel 3. Synthetic Ruby 4. Garnet 5. Red glass/paste

Given that eBay sellers might opt for less expensive alternatives, I would consider my gemstone authentic if it passed all tests.

Let’s get started!

5 | Red Glass / Paste

The most economical possibility is that I received plain red glass. A paste is simply a denser flint glass.

This hypothesis is easily dismissed since glass does not fluoresce under ultraviolet light. When exposed to a UV source, glass appears dark and somewhat purple. My ruby, however, lit up, indicating it was not glass.

4 | Garnet

Garnet is a silicate crystal with a variety of forms, each containing different metal combinations (chemical formula X?Y?(SiO?)?).

Like glass, garnet does not fluoresce under UV light, so it was also ruled out based on previous results.

Additionally, garnet exhibits magnetic properties. I borrowed a red garnet and discovered that a small neodymium magnet could exert a weak pull on it—quite unusual for gemstones!

3 | Synthetic Ruby

Next come the more challenging tests. The likelihood that my ruby is synthetic is high, as synthetic rubies cost significantly less and align with my purchase price. However, differentiating between natural and synthetic rubies is difficult since they possess identical chemical and structural properties.

The most reliable method involves examining for trace elements that indicate a lab-grown origin or inspecting for lab-induced structural defects under a microscope.

For more insights, I recommend this informative YouTube video by Thai Natural Gems detailing synthetic ruby characteristics.

Another interesting test utilizes a green laser. Both UV and green lasers can excite rubies to glow, but natural rubies typically emit a dimmer light than synthetic ones. Certain natural rubies with iron impurities may fluoresce less or not at all. A bright glow might suggest a synthetic ruby due to the absence of impurities.

My ruby emitted a bright glow under the green light, contrasting with my friend’s confirmed ruby, which did not fluoresce much at all. While not conclusive, this leans towards my ruby being synthetic.

Given the purchase price, it’s reasonable to suspect that my ruby is likely synthetic rather than a natural ruby being sold at a loss. However, there’s still one more contender to investigate…

2 | Spinel

The closest rival is red spinel, which shares many elements with ruby (chemical formula MgAl?O?). Their hardness levels are similar—8 for spinel and 9 for ruby—and they have comparable densities. For years, spinel and ruby were mistakenly classified as the same gemstone until a French crystallographer developed a distinguishing test in 1783.

Jean-Baptiste Louis Romé de l’Isle discovered that the angles between adjacent faces of natural crystals were consistently identical for the same gemstone. However, this method does not apply to pre-cut stones like mine.

Furthermore, the UV test fails to differentiate, as spinel also fluoresces under blacklight.

This leaves me with more complex testing methods. I could assess material properties such as the index of refraction (rubies bend light approximately 5% more than spinel) or heat conductivity. Speculatively, I believe spinel may not fluoresce under green light, while rubies typically do (any spinel owners interested in testing this?).

Ultimately, elemental analysis provides the most definitive differentiation between spinel and ruby.

1 | Natural Ruby

This final test would provide ultimate assurance regarding my ruby's authenticity, but it’s not something most individuals can perform at home. Fortunately, I know some knowledgeable friends.

A spectrometer is a scientific device that identifies the elements within a material. To verify my gemstone, I need to check for any unusually high concentrations of elements. Since rubies should only contain aluminum and oxygen, the presence of significant magnesium would indicate spinel rather than ruby.

Some spectrometers are destructive, but this one uses energy-dispersive X-ray spectroscopy, preserving the sample.

An emitter releases high-energy X-rays at the sample, displacing some electrons from the inner shells of the atoms. The vacancies are filled by more energetic outer shell electrons, emitting X-rays as they drop levels. By measuring the emitted X-ray’s energy, we can identify the specific atom since each atom has a unique orbital structure. This process allows us to determine the types of atoms in our sample—pretty fascinating!

The spectrometer output for my eBay ruby shows a composition almost entirely of aluminum and oxygen! With no magnesium peak present, I can confidently conclude that my gem is indeed a ruby, not a spinel.

Conclusion

I find gemstones incredibly beautiful. Ultimately, I believe my ring will be cherished even if the gem turns out to be just dyed glass. However, I’m relieved to confirm the authenticity of my gemstone and to tell my friend that, indeed, what I purchased from eBay is a genuine ruby!

Sources:

• Garnet info: https://en.wikipedia.org/wiki/Garnet
• More garnet info: https://www.ga.gov.au/education/classroom-resources/minerals-energy/australian-mineral-facts/garnet
• NYT article about spinel: https://www.nytimes.com/2020/02/10/fashion/jewelry-spinel-christies-sothebys-cartier.html
• Thai Natural Gems video about synthetic ruby: https://www.youtube.com/watch?v=LHN-H96QCwk