If you’ve ever been intrigued by the elegance and allure of gemstones, then black diamonds and onyx are two captivating gems you won’t want to miss. These gems have adorned jewelry and enchanted minds for centuries.

But what exactly are the similarities and differences between black diamond and onyx? That’s what we’re here to explore! We’ll delve deep into their distinct qualities while uncovering the subtle threads that tie them together.

As we journey into the heart of black diamond vs onyx, you’ll gain a newfound appreciation for the geological processes that form these treasures and the artistic ingenuity that brings them to life in stunning jewelry.

Whether you’re looking to expand your gem knowledge or simply indulge in the beauty of these gems, you’re in for an enlightening and enjoyable exploration!

Black Diamond vs Onyx – The Major Differences

They can be equally captivating and mesmerizing to look at, but if you compare onyx vs black diamond, you’ll find out that they share more differences than similarities.

Color – Black diamond has a deep, opaque black hue

Black diamonds and onyx are known for their distinctive colors and appearances. These contribute to their individual beauty and desirability.

Black diamond, as its name suggests, is known for its deep, opaque black hue. This intense black coloration is a result of numerous dark inclusions and impurities within its crystal lattice structure.

Although it’s named “black” diamond, it’s essential to note that it can sometimes exhibit secondary hues such as gray, green, or even dark brown. These can add depth and complexity to the gem’s overall appearance.

In contrast, onyx displays a different and distinctive range of colors. While it’s often recognized for its banded or layered appearance with alternating black and white bands, it’s not limited to just black and white.

Onyx can be found in various colors, including brown, red, and other shades. These bands of color create a captivating visual effect. It’s important to note the black and white banded onyx is perhaps its most well-known variety.

Luster – Onyx has a non-metallic luster

The luster, or the way light reflects off the surface of a gemstone, is another characteristic that sets black diamonds and onyx apart.

Black diamond often exhibits a submetallic to metallic luster. When light strikes its surface, it creates a shiny and reflective effect. This metallic luster enhances its overall appearance, giving it a striking and almost mirror-like quality.

The metallic shine of black diamond is one of the factors that contribute to its elegance and allure in jewelry.

Onyx, on the other hand, typically has a smoother, sometimes waxy, or vitreous (glassy) sheen. This non-metallic luster imparts a more subdued, yet still attractive, quality to the gemstone. It doesn’t have the same reflective brilliance as black diamonds but instead offers a smoother and somewhat softer visual appeal.

Onyx’s luster complements its banded or layered appearance, making it an excellent choice for carved jewelry and decorative items where the focus is on texture and pattern rather than intense sparkle.

Crystal Structure – Black diamond has a cubic crystal structure

A gem’s crystal structure plays a crucial role in determining its physical properties and appearance. In the case of black diamonds and onyx, their crystal structures differ significantly.

Black diamond has a cubic crystal structure, which is the same crystal structure as traditional colorless diamonds. This arrangement of carbon atoms contributes to its exceptional hardness and durability.

It also allows for the dispersion of light, which gives the diamond its renowned sparkle and fire. The cubic structure results in eight equally sized and oriented faces, enhancing its brilliance when properly cut and faceted.

Onyx, in contrast, falls into the category of microcrystalline or cryptocrystalline structures. It consists of tiny, tightly packed crystals that are too small to be seen individually without magnification.

This structure gives onyx a more uniform and smooth appearance, with no visible crystal forms. It also makes it an ideal material for carving and creating intricate jewelry designs because it can be shaped more easily.

Cleavage – Onyx has no cleavage

Cleavage refers to the tendency of a mineral to break along specific planes when subjected to stress. Under this property, black diamond and onyx also differ.

Black diamond has octahedral cleavage, which means it can potentially cleave or break along specific planes that intersect to form an octahedron.

However, in practice, the cleavage in black diamond is extremely rare due to its exceptional hardness. It’s challenging to exploit, as black diamond is incredibly resistant, making it highly durable and resistant to damage.

On the other hand, onyx lacks cleavage entirely. This means that onyx does not naturally break along specific planes like black diamonds or some other minerals. Instead, it tends to fracture in an irregular manner under stress or pressure.

This property makes onyx a more forgiving and workable material for artisans and jewelers, as they can shape it without the concern of cleavage planes affecting the final product’s integrity.

Composition – Black diamond is composed of carbon

The differences in composition between black diamonds and onyx are primarily related to their chemical makeup.

Black diamond is composed primarily of carbon atoms. Like in other diamonds, these carbon atoms are arranged in a cubic structure. What makes black diamond unique is the numerous dark inclusions and impurities within its carbon lattice.

These impurities, which often include graphite and sulfides, are responsible for its dark coloration. The specific types and concentrations of these impurities can vary, leading to variations in the secondary colors within the gem.

Onyx, on the other hand, is predominantly composed of silicon dioxide (SiO2), the same mineral composition as quartz. This gem is a variety of chalcedony, which is a cryptocrystalline form of quartz.

Its distinctive banded or layered appearance results from the alternating deposition of different mineral phases within its structure. The specific colors of onyx can be influenced by the presence of trace elements or impurities.

Formation – Onyx forms in sedimentary environments or cavities of volcanic rocks

The formation of both black diamond and onyx spans millions of years and occurs under specific conditions.

Black diamond, often referred to as “carbonado,” forms deep within the Earth’s mantle. The prevailing theory is that it originated from supernovae explosions, where immense pressure and heat transform carbon atoms into diamond.

This diamond is then brought closer to the surface during volcanic eruptions and carried within kimberlite or lamproite pipes. The journey to the surface is crucial, as it cools the gem and stabilizes its structure.

Meanwhile, onyx is associated with sedimentary environments and volcanic activity. It typically develops in the cavities or voids of volcanic rocks, often as the result of the slow deposition of silica-rich solutions. Over time, these solutions crystallize and harden, forming its distinctive banded or layered structure.

In some cases, onyx can also form as a result of metamorphism, where existing rock materials are subjected to heat and pressure, causing a transformation into onyx.

Hardness – Black diamond is the hardest known natural material

The hardness of gemstones affects their durability and usability. Black diamonds and onyx exhibit notable differences in terms of this property.

Black diamond is renowned for its exceptional hardness. It ranks at the top of the Mohs scale with a hardness of 10. This means that it’s one of the hardest natural materials on Earth.

Its hardness makes it highly resistant to scratching, which is a desirable quality for gemstones used in jewelry. It also means that it can withstand daily wear and tear without losing its luster or developing surface scratches.

Onyx, while still relatively hard compared to many other materials, is softer than black diamond. On the Mohs scale, it typically has a hardness ranging from 6.5 to 7. This places it in the same range as other varieties of chalcedony, such as agate.

This difference in hardness makes onyx slightly more susceptible to surface abrasions over time, particularly if it is exposed to harsh conditions.

Density – Onyx has a lower density

Density refers to the mass of a substance per unit volume. When comparing black diamond vs onyx, we can observe differences in their densities.

Black diamond is among the densest gemstones. Its density typically ranges between 3.2 to 3.5 grams per cubic centimeter (g/cm³).

This high density is a result of its carbon structure, where carbon atoms are tightly packed. Its dense structure contributes to its remarkable hardness and durability.

In comparison, onyx has a lower density. It typically falls in the range of 2.55 to 2.70 g/cm³. This is due to the composition of onyx, which has a less tightly packed atomic structure compared to the carbon lattice of diamonds.

While onyx is still relatively dense compared to many other materials, its lower density compared to black diamond is reflective of its distinct mineral composition.

Streak – Black diamond does not leave any streak

A streak is the color of the powdered form of a mineral when it’s scratched across a rough surface called a streak plate.

Black diamond does not leave any streak when tested on a streak plate. This absence of a streak occurs because its hardness, which ranks at the top of the Mohs scale, surpasses that of the streak plate used for testing.

On the other hand, onyx leaves a distinctive white streak when scraped against a streak plate. Its white streak is a notable contrast to its colored appearance.

This happens because the streak plate is typically made of unglazed porcelain, which is softer than onyx, allowing the gemstone to leave behind a fine white powder as it is scraped across the plate.

Fluorescence – Onyx has a weak fluorescence, if present

Fluorescence is a fascinating phenomenon in gemstones, where they emit visible light when exposed to ultraviolet (UV) light.

Black diamond often exhibits a typical bluish or greenish fluorescence under UV light. This fluorescence can vary in intensity and hue depending on the specific impurities and defects within the diamond’s crystal structure.

The presence of these impurities, such as certain types of boron, nitrogen, or other trace elements, is responsible for the fluorescence in black diamonds. This property can add to its allure, as it creates unique visual effects in certain lighting conditions.

As for onyx, it may also display fluorescence, but it’s generally weak compared to black diamond. When present, its fluorescence can vary depending on the specific composition of the stone, including the presence of trace elements.

The fluorescence in onyx is often not a primary feature or selling point for this gemstone, as it tends to be less noticeable compared to other gemstones.

Location – Black diamond is found in Africa, among others

The geographic locations where black diamond and onyx are found reflect the differences in their geological environments and mineral formations.

Black diamond has been discovered in several locations around the world, such as Brazil, Central African Republic, Australia, and Russia, among others. It’s typically found in alluvial deposits, which are sediments carried and deposited by rivers.

If you want to know where to find black diamond in the U.S., check out our article on that. You can also visit our guide to the best rockhounding locations near you.

Meanwhile, some significant deposits of onyx are found in Mexico, U.S., India, Brazil, and Pakistan, among others. It typically forms in cavities or voids within volcanic rocks or sedimentary environments. You can use our guide to the gem mines near you if you’re interested in finding onyx.

This difference contributes to the availability and distribution of these gemstones in the global market.

Price – Onyx is more affordable

Price is a crucial factor when it comes to evaluating gemstones, and black diamonds and onyx display notable differences in their price ranges.

Considered among the rarer and more valuable gemstones, black diamond’s price can range from hundreds to thousands of dollars per carat, and exceptionally large or top-quality stones can even exceed this range.

Specimens with a deep and uniform black color can also command high prices. In the world of high-end jewelry, black diamond is often featured as a centerpiece in engagement rings and other exquisite pieces.

In contrast, onyx is generally more affordable compared to black diamonds. The price of onyx can range from tens to hundreds of dollars per carat, making it a relatively affordable gemstone option.

While it can be used in a variety of jewelry pieces and decorative items, onyx’s cost tends to be more accessible to a broader range of consumers.

Black Diamond vs Onyx – The Similarities

While black diamond and onyx clearly have more differences, these two captivating gemstones also share a number of similarities, such as:

Magnetism – Neither black diamond nor onyx is magnetic

Both black diamond and onyx are non-magnetic, which means they do not exhibit any magnetic properties under ordinary circumstances. This lack of magnetism is due to their mineral composition and atomic structure.

Black diamond, composed primarily of carbon atoms, does not contain magnetic elements within its composition. Carbon itself is not magnetic, and black diamond does not have any impurities or inclusions that would induce magnetic behavior.

Similarly, onyx, primarily composed of silicon dioxide, lacks magnetic properties. Silicon dioxide is not a magnetic material, and onyx does not contain significant amounts of magnetic elements in its structure.

Conductivity – Onyx and black diamond are both insulators

Black diamond and onyx are both non-conductive gemstones. This means that they do not conduct electricity, and their electrical conductivity is essentially negligible.

Black diamond does not contain any conductive elements or impurities within its composition. Carbon, in its pure crystalline form as found in diamonds, is an excellent insulator, meaning it does not allow the flow of electricity.

Onyx, on the other hand, primarily consists of silicon dioxide with varying banding patterns. Silicon dioxide is also a non-conductive mineral and does not facilitate the flow of electrical currents as well.

This makes both black diamonds and onyx insulators. This property is not unique to these gemstones; in fact, most minerals and gemstones are non-conductive.

The Easiest Ways To Tell Black Diamond and Onyx Apart

If you’re wondering whether a certain specimen you’re in possession of is either a black diamond or an onyx, our discussion on their differences and similarities might help you a lot already.

But if you need more practical tips on how to tell an onyx vs black diamond, try the following:

Examine its color closely

Black diamond should have a deep and uniform black color, although it can occasionally display secondary hues like gray, green, or dark brown.

Onyx, meanwhile, typically features a banded or layered appearance with alternating black and white bands, although it can also come in other colors such as brown or red.

Observe its luster or shine

Black diamond often has a metallic or submetallic luster, which gives it a reflective and shiny surface.

But if you’re holding an onyx, you’ll observe that it does not have a metallic luster. Instead, it typically has a smooth, sometimes waxy or vitreous (glassy) sheen.

Perform a scratch test

Do a scratch test using a material with a known hardness. Black diamond is exceptionally hard, so it should not scratch easily.

Onyx is also relatively hard, but it’s not as hard as black diamonds and may be more susceptible to scratching over time.