Black Spinel vs Onyx: Your Complete Guide

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Black gemstones were once associated with mourning and gothic stereotypes. However, they’re now more acceptable and popular. More jewelry lovers now flaunt black gemstones, which has brought about a paradigm shift. Black gemstones now exhibit a sense of elegance and confidence. 

If you plan on buying a black gemstone jewelry piece, you might know of black spinel and onyx. You might even be curious about the difference between them. You don’t have to look any further, as this guide compares two of the most stunning black gemstones: black spinel and onyx. 

What is a black spinel?

black spinel ring -  Black Spinel vs Onyx: Your Complete Guide


Spinel (Mg,Fe)(Al,Cr)2O4 occurs as a mineral in igneous rocks and comes in various colors like red, lavender, violet, blue, green, and brown. But black spinel is the rarest of them all.

Black spinel is made of hard vitreous magnesium aluminium oxide or magnesium aluminate. 

Also known as ceylonite and pleonast, black spinel is opaque and untreated. The name ‘spinel’ is believed to come from the Latin word “spina”, which means “thorn”, referring to the sharp crystal formations on the gemstone.

This naturally occurring black gemstone is highly durable and offers high reflectance. Also, it’s a relatively hard stone, rating an 8 on the Mohs scale, which makes it a sought-after choice for everyday jewelry pieces.  

black spinel pendant

Spinel is most commonly found and mined in Burma, Cambodia, Thailand, and Sri Lanka. However, some traces have been found across Afghanistan, Brazil, Nepal, Madagascar, and Nigeria that suggest the existence of spinel. 

What is a black onyx?

black onyx ring - Black Spinel vs Onyx: Your Complete Guide


Onyx (SiO2) is formed of bands of chalcedony and is a relatively rare gemstone. It’s the semiprecious variety of agate with alternating parallel bands of color, composed of quartz and moganite. 

Its name is derived from the Greek word “onux”, which means “nail” or “claw”, referring to the mineral’s color. Moreover, it’s believed that black onyx is the fingernail of the goddess Venus that fell onto the earth.

14K Yellow Gold Onyx Cabochon And Black Diamond Ring

Natural onyx is found in various countries, including India, Germany, Australia, Madagascar, Argentina, Canada, and parts of the US. Onyx comes in many colors and black is one of the most common.

Onyx is perceived to be one of the most powerful gemstones known to humankind. In Feng Shui, black onyx protects the wearer from negative energy and offers stamina, determination, and support. Onyx is used in hand-carved jewelry and sculptures. 

Black spinel vs black onyx 

Now that you have a basic idea of these stunning black gemstones, let’s compare them thoroughly to help you learn their differences. 


black spinel gemstones


Black spinel is particularly striking out of all the black gemstones. This is because the stone has a black outer appearance. Under diffused light, black spinel could exhibit its natural color, such as purple, indigo, red, or blue — this distinguishes the black spinel from all other black gemstones. 

black onyx gemstones


Black onyx is quite fascinating as well. Its contrasting milky white agate formed by natural rhythmic crystallization on the dark background offers an intriguing, strong character and mystical aura. No wonder it’s a popular choice for carved cameos and intaglios owing to its spectacular layers that can be carved to show a color contrast. 


Black spinel is highly reflective and extremely lustrous. One can achieve even higher brilliance with cuts like oval, square, pear, or marquise. 

On the other hand, black onyx is known for its vitreous luster. It may appear glossy on the outside. However, black onyx beads are not polished within, making them dull inside. 


The black spinel stands at a solid 8 on the Mohs scale of hardness, making it highly durable. Also, it’s hard to scratch and chip, making it an excellent pick for daily wear.

On the other hand, Black onyx ranks 6.5-7 on the Mohs scale of mineral hardness. This makes it only moderately durable and thus requires proper care and storage to maintain its smooth and unaltered surface. 


Spinel is a semi-precious stone. However, black spinel gems aren’t very valuable as they’ve been mistaken for other types of gems for a long time, making them less popular among gemstone lovers. However, black spinel is becoming more popular with time. Also, it’s important to note that faceted spinels of all kinds tend to be more valuable than other precious stones. 

Onyx is also a semi-precious stone. Black onyx was once considered a precious gemstone. It’s still more valuable than other colors as it’s extremely rare. 


One carat of black spinel costs between $200 and $500, while one carat of black onyx costs between $25 to $100. The synthetic and treated varieties of onyx cost much less.


Other than being used for jewelry, black spinel is also known to repel negative energy — it’s believed to calm the wearer and evoke a sense of inspiration and empowerment. It helps the wearer easily let go of resentments and try to re-establish broken relationships. It’s also the August birthstone (along with peridot and sardonyx). 

Onyx is believed to be one of the most powerful gemstones ever. In Feng Shui, black onyx protects the wearer and wards off negativity. It’s known to provide stamina, determination, and support. Not to mention, black onyx is also used in hand-carved jewelry and sculptures.


Although ultrasonic and steam cleaners are considered safe for spinel, it’s better to clean your spinel jewelry with some warm soapy water. Consider wrapping each piece separately in a soft cloth when storing spinel jewellery to avoid scratches. 

Onyx gems often receive dye treatments so, it’s advisable to clean them with a soft brush, some mild detergent, and lukewarm water. Avoid using ultrasonic or other mechanical cleaning methods. While storing your onyx jewelry, wrap individual pieces in a soft cotton or velvet cloth. 

Black spinel vs black onyx: Chart

The chart below offers a quick comparison between black spinel and black onyx gemstones. 

FeatureBlack SpinelBlack Onyx
Formula (Mg,Fe)(Al,Cr)2O4SiO2
Hardness (Mohs Scale)6.5–7
DiaphaneityTransparent to opaqueTranslucent
Specific Gravity Usually 3.58 to 3.612.55–2.70
Refractive Index1.719 1.530 to 1.543
Price$200-$500 per caratAround $100 per carat

Frequently asked questions

If you still have questions regarding these gemstones, we’ve got you covered. We’ve answered popular questions to make things clear for you. 

Which is more expensive: Black spinel or black onyx?

Black spinel is generally more costly than black onyx, especially because it’s more durable.

Does black spinel look like a black diamond?

If you’ve never seen black spinel, you might mistake it for black diamond. Black spinel has been mistaken for black diamonds for years. However, they look different — while black diamonds have a metallic appearance, black spinel stones are highly reflective with a glass-like luster. 

Is black spinel the same as black onyx?

No, black spinel and black onyx have different compositions. Also, spinel is more durable and valuable than black onyx. 

Which should you choose?

If you want to add a black gemstone to your collection, spinel and onyx are great options. Onyx is an excellent choice for costume jewelry. However, if you wish to wear it daily, we recommend black spinel as it’s more durable. It’s more expensive than black onyx, but a well-made spinel jewelry piece will be worth it. 

Add some mystery to your jewelry collection

Black gemstones are eye-catching and elegant. And both black spinel and onyx are great picks that will give your jewelry collection an edgy yet elegant vibe. 

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