As a GIA Graduate Gemologist and jewelry appraiser, I often evaluate jewelry with an unknown history. Sometimes, identifying a gemstone is straightforward. Other times, a piece presents a true gemological mystery.

Today was one of those days.

A client brought me a beautiful family heirloom featuring an approximately 1-carat colorless center stone surrounded by smaller accent stones. The piece was purchased in Spain during the 1960s and is set in an interesting combination of sterling silver and 14-karat gold.

Before coming to me, my client had taken the piece to another jewelry store, where they were unable to confidently identify the center stone as a diamond.

The Investigation Begins

During my initial examination, I considered several possibilities. At first, I suspected the center stone might potentially be cubic zirconia, but it did not display enough of the characteristics I would expect to confidently make that identification.

Under magnification, the stone appeared exceptionally clean. However, closer microscopic examination revealed subtle straight internal features that provided an important clue and led me to investigate the possibility of corundum—the mineral family that includes sapphire.

Further gemological testing supported that conclusion.

The stone's optical properties were consistent with sapphire rather than diamond. Sapphire has a refractive index around 1.76–1.77, distinctly different from diamond's much higher refractive index of approximately 2.42.

Yet there was another interesting twist: the electronic diamond tester indicated diamond.

This is exactly why a handheld diamond tester should never be the only method used to identify an unknown gemstone.

The Final Identification: White Sapphire

After considering the stone's optical properties, microscopic characteristics, visual observations, and additional testing, I identified the approximately 1-carat center stone as a white sapphire—not a diamond and not cubic zirconia.

This was a tricky one!

Why You Shouldn't Rely on a Diamond Tester Alone

Electronic diamond testers can be useful tools, but they are only one part of a professional gemological examination. Depending on the type of tester, the stone, testing conditions, and other factors, a tester can potentially produce a result that requires further investigation.

A trained gemologist doesn't simply touch a tester to a stone and declare, "It's a diamond."

We look deeper.

A proper gemstone identification may involve examining:

• Internal characteristics and inclusions under magnification
• Facet junctions and surface features
• Optical properties
• Refractive behavior
• Reflection and brilliance patterns
• Thermal or electrical conductivity testing
• Polariscope reactions and optic character, when appropriate
• Additional gemological testing when the initial results conflict

When one test tells me "diamond" but other observations don't agree, that's when the real investigation begins.

The Importance of Professional Gemstone Identification

This family's heirloom had traveled from Spain in the 1960s and carried decades of history. Knowing exactly what the center stone is provides the family with a more accurate understanding of what they own and allows me, as their appraiser, to properly document and value the piece.

This case is an important reminder: Don't assume a colorless gemstone is a diamond simply because an electronic tester says so.

When identifying gemstones, every clue matters. A professional gemologist considers the complete picture, compares multiple test results, and continues investigating until the evidence supports a reliable conclusion.

Do you have an inherited ring, necklace, or family heirloom with a gemstone you've never been able to identify?

It may have a story—and an identity—you haven't discovered yet.

Legacy Jewelry Appraisers & Buyers
Professional Jewelry Appraisals • Gemstone Identification • Estate Jewelry Evaluations

Gina Watson, GIA Graduate Gemologist

By Appointment Only