How to Tell if Black Onyx is Real – 3 Easy Methods

Last Updated on December 29, 2023

Quickly becoming one of fashion’s most sought after gemstones, black onyx has taken center stage with its dazzling and deep tones that are perfect for necklaces, rings, and bracelets. 

But the rising popularity of black onyx comes with a dark side: an increasing number of counterfeit sellers are trying to mimic the stone’s rare and natural beauty with low-cost fake alternatives while passing the cost onto buyers.


How to tell if black onyx is real?

Like many other highly desirable gemstones, black onyx is a commonly counterfeited stone sold by disingenuous gemstone dealers looking to get rich quick.

In order to tell if black onyx is real, pay attention to the overall appearance of the stone.  An authentic piece of black onyx will exhibit a waxy luster, have an opaque transparency, and may appear glossy when polished, while a fake piece of black onyx will appear shiny like glass.

Black onyx will present with parallel bands of white and black lines above the base of the stone depending on the size of the stone and should be free of chips and cracks on the stoneface.

How to test if your black onyx is real?

After thoroughly inspecting the overall appearance of the black onyx stone for the correct sheen and patterns, further confirm the authenticity of the piece by using three simple techniques:

1. Black Onyx scratch test

Because black onyx registers 6.5 to 7 on the Mohs scale, the stone is scratch resistant to materials that fall lower on the scale. 

To test if your black onyx is real or counterfeit, scratch the surface of the stone with an item ranging from 1-6.5 on the Mohs scale, such as a fingernail, copper penny, or steel knife. 

If the object leaves a scratch on the stoneface, the stone in question isn’t authentic black onyx, but still may make for a cute piece of jewelry.

2. Heat the stone

Black onyx is a reasonably durable stone that can withstand high temperatures of heat up to 1000 degrees.

To test your black onyx piece for authenticity, use a lighter and gently heat the surface of the stone for 10 seconds before dropping into a glass or bowl of water. 

If the stone remains unchanged, there’s a good chance it’s the real deal.  If the piece appears melted or damaged in any way, it isn’t black onyx.  

3. Surface check

Black onyx has a distinctive appearance that sets it apart from other stones. 

A black onyx stone will appear well-polished and reflective with a waxy luster.  The surface of the black onyx piece will be free from cracks and scratches and may present with parallel bands of white lines depending on the size of the stone. 

What is black onyx?

Black onyx is a flat-layered variety of chalcedony, a microcrystalline type of quartz that comes in a variety of forms, colors, and patterns. 

Formed inside of caves by silica-rich waters seeping through the cracks and fissures in other rocks, black onyx displays unique parallel layers of black and white bands throughout the semi-precious stone. 

Natural onyx comes in a variety of colors, including red, green, blue, gold, brown, and black and can be found in many places including Uruguay, India, South America, and Germany.

Because black onyx registers at 6.5 to 7 on the Mohs scale, it’s an exceptional choice for carved gemstones and beads.

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Commonly asked questions about Black Onyx

When considering purchasing a piece of black onyx,  you may find yourself asking:

How do I identify black onyx?

To identify black onyx, focus on the stone’s appearance.  Black onyx has a waxy texture, although it may appear glossy when polished. The surface of black onyx should feel cool to the touch and be free of blemishes, such as cracks and chips.

Black onyx will have parallel bands of black and white running above the base of the stone.  The stone is dense and has a weighted feeling when held in the palm of the hand.

How do I tell black onyx from glass?

Onyx and glass can easily be misidentified as one another.  To tell the difference between glass and onyx, try placing the piece near your lips.  If the piece begins to feel warm, it’s likely glass. 

If working with beads, inspect the area around the mouth of the bead for dimpling, which typically happens with glass. 

Lastly, take a small piece of the stone and place it inside a covering on a safe surface.  Using a hammer, gently break apart the piece.  If the broken pieces appear shiny rather than dull, the material is likely glass.

Does black onyx scratch easily?

No, black onyx is a low-maintenance and highly durable stone that does not scratch easily.  Black onyx should be carefully stored in a box or pouch when unworn and kept away from harsh chemicals and materials registering higher than 7 on the Mohs scale, such as diamonds. 

With the proper cleaning and care, black onyx can last for many years.

Ready to buy black onyx?

Black onyx is a versatile and unique stone that boasts durability and depth.  With its rich tones, smooth texture, and distinctive patterns, black onyx is the perfect addition to any collection looking for a unique stone. 

Purchasing a piece of black onyx can be a worry-free experience with the proper set of tools to help identify counterfeit stones.  Inspecting the appearance of the stone and performing the scratch and heat tests can help identify authentic black onyx from its counterfeits and help you confidently purchase your perfect piece of black onyx.

Eran Hayo is the Chief Editor of Jewels Advisor, with over 5 years of experience in the fields of jewelry and memorabilia. He built Jewels Advisor to serve one main purpose – to teach you everything he knows about jewelry, and help you make better-informed decisions when buying diamonds and engagement rings online. His work has been cited on famous publications such as The Sun, MSN and WikiHow.