Blue Gemstone Mysteries: A Gemologist's Guide to Identification
As a gemologist, some of the most challenging stones to identify are light blue gems. To the untrained eye-and often even to an expert without the right tools-a light blue stone can be a total mystery. It could be aquamarine, blue topaz, blue spinel, or even a synthetic stone or glass. The value of these gems vary dramatically, making accurate identification crucial for any jewellery buyer.
Today, I'm taking you behind the scenes to show you my process for identifying these tricky gems and explaining why it matters.
Why Are Light Blue Gemstones So Difficult to Identify?
The primary challenge is the lack of visible clues. Unlike other gems, light blue stones often have very few, if any, inclusions or internal imperfections. This means you can't rely on a jeweller's loupe alone to tell you the stone's identity. Even a piece's style, like a classic mid-1900s design, doesn't offer a definitive hint, as all these stones were popular in vintage jewellery from that era.
The Value Spectrum: Natural vs. Treated vs. Synthetic
Before we get to testing, let's understand why we care so much about what these stones are. The value difference is staggering:
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Aquamarine: The most valuable and desirable of the light blue gems. It is a variety of beryl - the same gemstone family as emeralds - and is prized for its soft, watery blue colour.
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Blue Topaz: This is an abundant stone, but almost all blue topaz jewellery you see has been irradiated to achieve its colour. Naturally occurring blue topaz is incredibly rare and valuable, but irradiated blue topaz is far more common and affordable.
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Synthetic Spinel & Glass: These stones have a very low value. They are lab-created to look like natural gems but lack any intrinsic value beyond their decorative appeal.
My Testing Process: A Gemologist’s Toolkit
A good gemologist is trained to know the fastest and most reliable route to get to a definitive answer. For light blue gemstones, a refractometer is the ultimate tool, but it's not always the first step. Here's my typical route:
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Visual Inspection: First, I look for any variations in colour. Aquamarine can have a secondary and subtle green tone, whereas topaz can reach deeper but less icy blues.
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Polariscope: A quick check with a polariscope is a great way to rule out glass and synthetic spinel, as both have distinctive results under the polariscope. If the stone goes light and dark four times in a full rotation, it confirms it's a crystalline gem.
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Chelsea Colour Filter: This is the key to a quick initial diagnosis for these specific
stones. When you shine a light through this filter, aquamarine will often appear green or greenish, while blue topaz and many synthetics will appear pink or colourless. This is a powerful indicator that guides the next step of testing.
In the jewellery suite I was testing, the results were surprising! The test revealed that what looked like a matching set of jewellery actually contained different stones- one earring and the ring were aquamarine, but another earring was topaz! The bracelet also showed mixed results, which is a strong signal to proceed with a refractometer for a conclusive answer.
The Refractometer: Why It’s the Final Step
So why not just use the refractometer from the start? Because it can be time-consuming, and a good gemologist knows how to use other tools for quick, reliable clues. The Chelsea Colour Filter provides a strong indication of what a stone might be, allowing me to focus my final testing on the pieces that require a definitive, diagnostic result.
Understanding your gemstones is an essential part of becoming a smart jewellery collector. Always buy from a reputable jewellery retailer who is transparent about their testing and can provide you with a detailed, professional assessment of the stones you are considering.
