Black Agate vs Onyx (Differences to Know)

Black agate and onyx both are varieties of chalcedony, a mineral which is part of the quartz family.  If you look closely at each stone, it can look quite similar; however, there are differences.  In fact, there’s often confusion, as black agate and black onyx are confused with other types of black stones.

In today’s guide, let’s talk about the key differences and similarities between black agate and onyx.  Hopefully, by the time you’re done reading it, you will be able to distinguish between the two.

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What is the difference between black onyx and black agate?


One of the main differences between black agate and onyx is the appearance.  A black agate is often solid in color, sometimes with slight white or gray banding like almost all agates.  After all, agates are defined by their banding.  Black onyx will only have parallel banding, but it will always be solid black and/or white. To make it easier, agates will be more of a ring-like banding, whereas onxy will be straight.

It’s also opaque, which simply means light can’t pass through, whereas black agates, and all agates for that matter, are translucent, which means light can pass through.  Lastly, a black onyx will have more of a waxy luster, whereas a black agate is more of a glass-like luster.


Another key difference to note here is the durability.  All agates, including black agate, are relatively hard, measuring 6.5-7 on the Mohs hardness scale.  The higher the number is, the less susceptible it is to scratching.  Black onyx is a pinch softer, measuring a 6-7 on the Mohs hardness scale.  While they are both durable in a sense, black agate is more resistant to scratches than that of black onyx.  The only way one of these stones can scratch is if it comes in contact with a stone with a higher hardness.


Black agate is formed when holes are filled inside of a basalt stone with mineral-rich fluids.  It is then when the fluids solidify and starts to form the agate.  Black onyx is a  microcrystalline crystal, which means the small crystals are only seen with a microscope.  This stone is formed inside the gas bubbles of a volcanic rock.

Geographical Location

In general, agates are found almost all around the world, and it’s the reason it’s referred to as the “earth stone.”  While they are found all over, black agate is mostly found in Brazil and Mexico.  Black onyx, however, isn’t found throughout the world, as it’s mainly found in Brazil, Canada, India, Madagascar and Pakistan.


There are differences in metaphysical properties between the two as well.  Black agate is said to be more of a ground and stabilizing stone, and this can be said for most agate stones.  If you were to wear it, they say you should feel more level headed and focused, even giving you a sense of calmness.  Black agate is said to help protect you from negative energy as well as attract good luck in life.  Wearing it is also said to help repel any negative energy you may be experiencing.

Black onyx, on the other hand, can help with grounding and protection like agate, but it’s said to be a better stone if you’re looking for a stone that helps with emotional balancing.  It’s even said to be a good stone if you want help dealing with grief or separation in life.  Wearing this stone is said to help enhance your feeling as well as ease your feelings of sorrow.

Is black agate and onyx the same?

As mentioned, both are varieties of layered chalcedony and quartz, but the biggest difference is that agate will have curved bands, all of which vary in almost every color.  Onyx will have a higher density of silica elements, such as quartz.  Both are a component of two or more elements, and these are the only two gemstones to have layers of chalcedony.

Both are black, of course, but, as mentioned, agates can occur in various colors, whereas onyx will only be black, gray or white, mainly.  The black you see in black agate will come from the chemical compounds of iron, and with agates, it’s the minerals within that determine the colors.  The color differences you’re able to see are mainly caused by the microscopic inclusions of iron and manganese

One close similarity to note is that they both are said to stimulate the root chakra, which is said to be connected to the Earth, which helps you feel secure.  It is this chakra that’s able to balance your feelings, taking away any negative energy in your life.  Both of these are said to help relieve stress, anger and anxiety.

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About Me

Hi! I'm Lauren, and I run Moonlight Gems AZ. I'm an avid crystal collector and would love to share my expertise with you.