How To Tell If A Gemstone Is Real

At N.T. Ferro Jewelers, we pride ourselves on a legacy of craftsmanship and authenticity that has been the cornerstone of our family-owned business since 1947. Understanding the authenticity of gemstones is crucial for anyone looking to invest in fine jewelry. With our expertise, we aim to empower you with the knowledge to identify genuine gemstones, ensuring that your selection is both beautiful and genuine. This guide offers practical tips and insights into distinguishing real gemstones from imitations, enhancing your confidence and appreciation for these natural wonders.

Visual Inspection: Color and Clarity

Saturation and Uniformity

Genuine gemstones typically display a color that is consistent and evenly distributed throughout the stone, though some natural variations can exist. Overly bright or perfectly uniform colors can sometimes indicate synthetic or treated stones. It's important to compare the stone in question with verified samples to assess its color quality.

Natural Inclusions

Most natural gemstones contain inclusions. Using a magnifying glass or jeweler's loupe, examine the stone for tiny flaws or irregularities inside it. While a flawless stone might seem ideal, a complete lack of inclusions can often signify a synthetic or lab-created stone.

Physical Properties: Hardness and Density

Hardness Testing

The hardness of a gemstone, measured on the Mohs scale, indicates its ability to resist scratches. Diamonds, the hardest natural substance, can scratch most materials, unlike softer gemstones such as opal or turquoise. However, performing hardness tests can risk damaging the gemstone, so it is generally recommended that these tests be conducted by professionals who can assess the stone without causing harm.

Density Analysis

Density or specific gravity can also help identify a gemstone, with genuine stones typically feeling heavier than their synthetic counterparts. Accurate density measurement requires precise scales and careful comparison against standard values for each type of gemstone. While useful, density alone does not definitively determine authenticity, making professional evaluation a crucial step in verifying a gemstone’s true nature.

Light Tests: Optical Phenomena

1. Pleochroism

Pleochroism is an optical phenomenon in which a gemstone exhibits different colors when viewed from different angles. This effect is particularly evident in anisotropic gems, such as tanzanite and iolite, which have different optical properties along different axes. By rotating the gemstone under a polarized light source, our gemologists can observe changes in color, which is a strong indicator of the stone's natural origin.

2. Chatoyancy (Cat's Eye Effect)

Chatoyancy, or the cat's eye effect, is seen in gemstones that contain parallel fibrous inclusions or channels. When light strikes these inclusions, it is reflected in a narrow band that appears to glide across the stone as it is rotated. This effect is commonly associated with chrysoberyl, tiger's eye, and certain types of tourmaline. Observing a sharp, well-defined cat's eye line under a direct light source can confirm the presence and quality of these inclusions, suggesting a genuine gemstone.

3. Dispersion and Fire

Some gemstones, like diamonds, are highly valued for their dispersion or fire, which is the splitting of white light into its constituent colors. This creates a play of spectral colors within the stone. A real diamond will display a vivid fire, which can be assessed under a direct light source. Synthetic diamonds and look-alike materials often have different levels of dispersion and may not replicate the same colorful sparkle.

Heat Tests: Response to Thermal Changes

1. Thermal Conductivity

Diamonds are known for their remarkable thermal conductivity, meaning they can dissipate heat rapidly. At N.T. Ferro Jewelers, we use thermal conductivity testers to differentiate diamonds from their simulants. A real diamond will carry heat away from the source quickly, causing the tester to indicate a high reading, whereas synthetic replicas will show lower conductivity.

2. Reaction to Heat

Some gemstones change color or clarity temporarily when exposed to heat. For example, real aquamarine may become more blue or transparent with gentle heating, which reverses as it cools. However, conducting heat tests can be risky and should always be performed by a professional to avoid damaging the gemstone. Excessive heat can cause fractures or permanent color change in some gems.

Advanced Equipment Used in Gemstone Testing

1. Refractometer

A refractometer is an essential tool in gemology used to measure the refractive index of a gemstone. The refractive index is a unique number that indicates how much light is bent, or refracted, when entering a material. Each mineral has a characteristic refractive index, and by measuring this, gemologists can often determine the type of gemstone. For instance, the refractive index can help distinguish between diamond and its look-alikes like cubic zirconia or moissanite, each of which has a different value.

2. Spectroscope

The spectroscope is another vital instrument in a gemologist’s toolkit. This device allows the observer to see the spectrum of colors absorbed by the gemstone. Each gemstone has a unique absorption pattern, which can be thought of as its spectral fingerprint. By analyzing these patterns, gemologists can identify various gemstones and detect the presence of treatments or dyes meant to enhance or alter their appearance.

3. Microscope

A high-powered gemological microscope provides a detailed view of the internal and external structure of the gemstone, enabling the identification of inclusions, growth patterns, and craftsmanship details that are not visible to the naked eye. Inclusions, while sometimes seen as flaws, can be key indicators of a gemstone’s authenticity, as synthetic stones often lack the minute, natural inclusions of their genuine counterparts.

4. Polariscope

The polariscope is used to determine the optical properties of a gemstone, specifically its isotropic or anisotropic nature. This can help in identifying single-refractive and double-refractive stones and can be crucial in differentiating between natural gemstones and synthetics or imitations.

5. Loupe

A loupe is a small, portable magnifier used by jewelers and gemologists to inspect gemstones. It allows for a closer examination of the surface and internal structure of the stone, helping to identify minute details that indicate quality, treatment, or manipulation.

Obtain Gemological Certification

For a definitive authentication, consider a professional gemological examination and report from certified laboratories. These reports can provide a detailed analysis of the gemstone’s characteristics and confirm its authenticity.


Knowing how to verify the authenticity of gemstones is essential for anyone passionate about fine jewelry. At N.T. Ferro Jewelers, located in the scenic and inspirational setting of Woodstock, Vermont, we are here to provide guidance, expertise, and a personalized shopping experience. We invite you to visit our store to explore our exquisite collection of genuine gemstones and to discuss how we can help you create a piece that is truly your own. Remember, choosing a real gemstone is not just about beauty—it’s about making an informed, confident choice that reflects your values and style.