How do you know if onyx is real? Tips from the Experts 


Embarking on a journey to uncover the authenticity of onyx is akin to setting out on an adventurous road trip through the diverse landscapes of the gemstone world. Just as a seasoned travel driver navigates winding roads and hidden paths, you too will learn to discern the genuine from the imitation with expert precision.

Onyx, with its striking bands of black and white, has long been a symbol of elegance and mystery. However, the market is flooded with synthetic and counterfeit versions, making it essential to distinguish the real from the fake. This guide serves as your roadmap, offering expert tips and techniques to ensure your onyx is authentic.

What is Onyx?

Onyx is a variety of chalcedony, a mineral in the quartz family. It is characterized by its parallel banding, which can come in a variety of colors, although black and white are the most common. Onyx has been used in jewelry, carvings, and decorative items for thousands of years, prized for its beauty and durability.

How Can You Tell if Onyx is Real?

Key Characteristics of Genuine Onyx To determine if onyx is real, you need to look for specific characteristics that are unique to this gemstone. Here are five key aspects to consider

  1. Color and Banding

Genuine onyx typically features parallel bands of color. The most common color combination is black and white, but onyx can also come in other colors such as red, brown, and green. The bands should be distinct and evenly spaced. If the colors appear too uniform or the bands are irregular, it may be a sign of a synthetic or imitation stone.

  1. Hardness
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Onyx has a hardness of 6.5 to 7 on the Mohs scale. This means it is relatively hard and can scratch glass. To test the hardness, you can try scratching the surface of the stone with a piece of glass or a steel knife. If the stone scratches the glass, it is likely to be genuine onyx.

  1. Luster

The luster of onyx is typically vitreous, meaning it has a glass-like shine. When polished, genuine onyx should have a smooth, reflective surface. If the stone appears dull or has a waxy luster, it may not be real onyx.

  1. Weight

Onyx is denser than many imitation stones. When you hold a piece of genuine onyx, it should feel heavier than a similarly sized piece of plastic or resin. This weight difference can be a helpful indicator of authenticity.

  1. Temperature

Natural stones, including onyx, tend to feel cool to the touch. If you hold the stone in your hand and it feels warm or room temperature, it may be an imitation made from plastic or glass.

Onyx is Real

Advanced Testing Methods

While the above characteristics can help you identify genuine onyx, there are more advanced methods that can provide additional confirmation.

  1. Magnification

Using a jeweler’s loupe or a microscope, examine the surface of the stone. Genuine onyx will have natural imperfections, such as tiny inclusions or irregularities in the banding. Synthetic stones often have a more uniform appearance with fewer imperfections.

  1. UV Light

Under ultraviolet (UV) light, genuine onyx may exhibit a slight fluorescence, typically a greenish or bluish hue. This is due to the presence of trace minerals within the stone. Imitation stones may not fluoresce or may exhibit a different color.

  1. Specific Gravity Test
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The specific gravity of onyx is between 2.55 and 2.70. To perform a specific gravity test, you will need a scale and a container of water. Weigh the stone in air and then weigh it while submerged in water. The specific gravity can be calculated using the formula

$$ \text{Specific Gravity} = \frac{\text{Weight in Air}}{\text{Weight in Air} – \text{Weight in Water}} $$

If the result falls within the range for onyx, it is likely to be genuine.

Common Imitations and Synthetics

Types of Imitation Onyx

There are several materials that are commonly used to imitate onyx. Understanding these can help you better identify genuine onyx.

  1. Dyed Agate

Agate is another variety of chalcedony that can be dyed to resemble onyx. Dyed agate often has a more uniform color and less distinct banding compared to genuine onyx. The dye can sometimes be detected by examining the stone under magnification or by using a solvent to see if the color bleeds.

  1. Glass

Glass can be molded and colored to mimic the appearance of onyx. However, glass is typically less dense and has a different luster compared to genuine onyx. It may also have air bubbles or other imperfections that are not found in natural stones.

  1. Plastic and Resin

Plastic and resin are lightweight materials that can be used to create imitation onyx. These materials often feel warm to the touch and lack the density and hardness of genuine onyx. They may also have a different luster and can be easily scratched.

Buying Genuine Onyx

Tips for Buying Genuine Onyx

  • Purchasing from Reputable Sources
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One of the best ways to ensure you are buying genuine onyx is to purchase from reputable sources. Look for established jewelers or dealers who have a good reputation and provide certification for their stones.

  • Asking for Certification

When buying onyx, ask for a certificate of authenticity from a recognized gemological laboratory. This certificate should provide details about the stone, including its origin, color, and any treatments it may have undergone.

  • Educating Yourself

The more you know about onyx, the better equipped you will be to identify genuine stones. Take the time to learn about the different types of onyx, their characteristics, and the common imitations. This knowledge will help you make informed decisions when purchasing onyx.


Knowing how to tell if onyx is real is essential for anyone who appreciates this beautiful gemstone. By understanding the key characteristics of genuine onyx and using advanced testing methods, you can confidently identify real onyx and avoid imitations. Remember to purchase from reputable sources, ask for certification, and educate yourself about onyx to ensure you are getting a genuine stone. With proper care and maintenance, your onyx will continue to be a stunning and cherished part of your collection for years to come.