You know that diamonds score a “10” on the Mohs scale of mineral hardness, including black diamonds, which are generally considered tough and durable. You might also be aware that diamonds, in general, are great conductors of heat.
But what about electrical conductivity? Do black diamonds conduct electricity?
Inclusions that give black diamonds their color are graphite, and graphite is a great conductor of electricity. Thus, some black diamonds can indeed conduct electricity.
That’s just the short version of the answer. In this article, we’ve covered everything you need to know about these black-colored gems and their electrical conductivity. Let’s dive in!
What Is Electrical Conductivity?
Electrical conductivity is, simply put, a measurement of how easily a particular material allows an electric current to flow through it. On the flip side, electrical resistivity measures how heavily a material resists the flow of electric current.
Great electrical conductors are often good conductors of heat, too; it’s evident in most metals. Interestingly enough, the temperature of a material can impact its electrical conductivity in a not so straightforward manner:
For materials known as conductors, a temperature increase would generally decrease their conductivity – and vice versa. However, for insulators, the rise in temperature would increase their conductivity.
This relation between electrical conductivity and temperature is generally helpful in the creation of materials known as superconductors.
Now, the two most common techniques for measuring electrical conductivity are two-point and four-point methods:
The two-point method involves passing an electrical current through a sample of the material. The current is delivered by two copper nodes that are attached to the ends of the bar, and the amount of electrical current that flows through the bar is measured.
The four-point method is fundamentally error-prone. The issue is that the measuring equipment has properties that are being measured at the same time as the testing material. So, that means that the measured electrical conductivity is usually lower than it really is.
This technique mitigates most of these errors by using a voltmeter connected to the sample separately from the ammeter connected to the ends. The electrical current flows through the piece and is measured by the ammeter, while the voltmeter tracks the voltage.
Let’s Talk About Black Diamonds
Black diamonds, also known as carbonados, are made of hard crystallized carbon, just like any other diamond. However, the black diamond color is created somewhat differently from the rest of the diamond family.
Natural black diamonds get their color as a result of graphite inclusions. If the level of inclusions is high enough, it makes the whole stone black.
And that results in a unique gem that has recently become more and more popular. It’s fascinating to think that these so-called “imperfections” give black diamonds their unique beauty, huh?
Of course, natural black diamonds are not the only option.
On the other hand, treated black color diamonds can be irradiated to look black, but in reality, they’re a very dark green color. The gems can also be subjected to other high-temperature and low-pressure annealing, which induces a large graphitization.
Natural black diamonds are notoriously known to be hard to cut and polish. They have irregular growth patterns due to the fact that they’re polycrystalline or aggregates of numerous diamond crystals. The countless graphite inclusions could cause pits, making black diamonds tricky to polish.
Even more so, because of this, black diamonds also tend to chip or break during the cutting process. They can generally take much longer to facet than their white or colorless counterparts – and the finished gemstones are more easily damaged.
Anyway, back to our main point – graphite inclusions: These graphite inclusions are so pronounced and prevalent in some black diamonds that these gems become electrical conductors through the graphite.
What Is Graphite?
Graphite is also a naturally occurring form of crystalline carbon. It’s an element mineral found in igneous and metamorphic rocks. Graphite is recognized as a “mineral of extremes”:
It’s extremely soft, cleaves with very light pressure, and has a very low specific gravity. On the other hand, graphite is extremely resistant to heat, and it’s nearly inert in contact with almost all minerals.
These properties give it a range of uses in manufacturing and metallurgy.
Graphite is a mineral that forms when carbon is subjected to pressure and heat in the upper mantle of the Earth’s crust. Sounds familiar?
Most of the graphite found at the Earth’s surface was created at convergent plate boundaries. That is where organic-rich shales and limestones were put under the great heat and pressure of regional metamorphism.
That also resulted in creating marble, gneiss, and schist that contained tiny crystals and flakes of graphite.
When graphite is in high concentrations, these rocks can be mined. After that, they are crushed to a particle size that frees the graphite flakes, after which it’s processed through specific gravity separation to remove the graphite of the lower density.
Some graphite is created from the metamorphism of coal seams. The organic material found in coal is composed mainly of carbon, hydrogen, oxygen, sulfur, and nitrogen.
The heat of metamorphism breaks up the organic molecules of coal, volatilizing hydrogen, oxygen, nitrogen, and sulfur. And what remains after is an almost pure carbon material that crystallizes into the mineral we know as graphite.
This graphite occurs in seams that resemble the original layer of coal.
During the mining process, the material is known as amorphous graphite. Interestingly enough, the word “amorphous” is incorrect here as this graphite does have a crystalline structure.
This material looks similar to lumps of coal but without dull and bright banding.
A small fraction of graphite is formed by the reaction of carbon compounds in the rock during the hydrothermal metamorphism. This carbon can be found in veins of hydrothermal mineral deposits.
And thanks to that high degree of crystallinity, graphite has become the preferred material for numerous electrical uses.
As we mentioned earlier, a small amount of graphite is known to occur as a primary mineral in igneous rocks – tiny particles in basalt flows. Additionally, it can form in pegmatite – and some iron meteorites contain traces of graphite, as well.
These forms of graphite don’t have any economic importance, though.
But if there’s one thing we’ve learned, it’s that graphite seems to be everywhere!
Graphite Vs. Diamonds: Things To Remember
Everybody should know by now that graphite and diamonds are two mineral forms of carbon.
Diamond is formed in the Earth’s mantle under extreme heat and pressure. On the other hand, graphite found near the surface of the Earth is formed within the crust at lower pressures and temperatures.
Graphite and diamond have the same composition – but have very different structures.
The carbon atoms in graphite are connected in a hexagonal network which builds sheets that are precisely one atom thick. These sheets are rather poorly linked and easily cleave or slide over one another if put through a small amount of force.
That gives graphite a very low hardness, its slippery feel, and perfect cleavage.
On the other hand, the carbon atoms in diamonds are connected into a frameworks structure. Every atom is connected into a three-dimensional network with four other atoms with strong covalent bonds.
This arrangement holds carbon atoms firmly in place, which is what gives diamonds their exceptional hardness.
While we’re on the topic of graphite, let’s quickly cover its synthetic counterpart.
Synthetic graphite is made by heating materials high in carbon, such as petroleum coke and coal tar pitch, to temperatures over 2500 degrees Celsius.
Every volatile material and many metals in the feedstock are separated or destroyed at these high temperatures. The graphite that remains connects into a sheet-like crystalline structure.
This graphite can have purity over 99%, and it’s used in products where this extremely pure material is needed.
Beyond Black Diamonds: Are There Other Gems That Conduct Electricity?
Compress certain crystals, and you can make electric current flow through them. The reverse is typically true, too, and if you pass electrical current through the same crystals, they’d “squeeze” themselves by vibrating.
That is pretty much piezoelectricity in a nutshell – but let’s have a formal definition for the sake of science: Piezoelectricity is the occurrence of an electrical potential across the sides of a crystal when you put it through mechanical stress.
In practice, the crystal acts like a tiny battery with a negative charge on one face and a positive charge on the opposite face; electric current flows if you connect the two faces to make a circuit.
The most common piezoelectric conductors are quartz, tourmaline, and topaz. Now that we know that there are gemstones that can conduct electricity – let’s talk about them.
What Is Quartz?
Quartz is a widely distributed mineral composed primarily of silica or silicon dioxide. Smaller impurities such as potassium, sodium, lithium, and titanium can be present. Quartz has great economic importance.
Many varieties of quartz are actually gemstones, including citrine, amethyst, rose quartz, and smoky quartz. Sandstone, composed mainly of quartz, acts as an essential building stone.
Large amounts of sand quartz are used in the production of glass and ceramics. Crushed quartz is used as the abrasive in sandpaper. Silica glass, also known as fused quartz, is used in optics to transmit UV light.
Various vessels made of silica glass have essential applications in labs, too.
Quartz is known to be the second most abundant mineral found in the Earth’s crust – right after feldspar. Quartz appears in almost all acid igneous, sedimentary and metamorphic rocks. It’s an essential mineral in silica-rich felsic rock such as granites, granodiorites, and rhyolites.
Related Read: Diamond Vs. Quartz: Comparison Guide
What Is Tourmaline?
Tourmaline is a borosilicate mineral of the variable and complex composition and can be found in three types – iron tourmaline, magnesium tourmaline, and alkali tourmaline.
Some crystals are pink, and others can be green. These colored variants, when transparent, are cut as gems.
In addition to its aesthetic use as a gem, tourmaline plays a role in pressure devices because of its piezoelectric properties. It has also been used in depth-sounding devices and similar gadgets that detect and measure variations in pressure.
Because the tourmaline is resistant to weathering, it collects in detrital deposits. It’s also a common “accessory mineral” in many sedimentary rocks.
In case you’re interested, gem-quality pegmatites are found in the US, Brazil, and Madagascar.
What Is Topaz?
Topaz is a silicate mineral that is valued as a gemstone. It’s an aluminum silicate that contains fluorine. Topaz is formed by fluorine-bearing vapors radiated during the last stages of igneous rock crystalization.
It usually occurs in cavities in granite and rhyolites, and high-temperature veins. Topaz is often associated with cassiterite as it can be helpful to show the presence of that tin ore.
The finest topaz is found in the Cairngorm Mountains in the Central Highlands. On that note, the famous topaz rock of the Schneckenstein, Germany, yields the pale yellow crystals that were once cut for jewelry.
Fine topaz can also be found at several locations in Siberia and the Urals. Another location that yields beautiful crystals is Takayama and Tanokamiyama in Japan. Other countries that have fine topaz are Brazil and the US.
Pure topaz can be colorless, and it can be mistaken for a diamond when it’s a brilliant cut. It also comes in a few colored variants, such as yellow, blue, or brown. The primary use of topaz today is in jewelry.
If somebody asked you, “Do black diamonds conduct electricity?” would you know the right answer? Well, after reading this guide, we sure hope you would.
Since each outer shell of every carbon atom in diamond creates a covalent bond, forming a rigid structure, there are no free electrons available for transporting the charge. Well, that’s the case with white or colorless diamonds, anyway.
However, when it comes to black diamonds, they have graphite inclusions within them. Graphite is known to be an excellent electric conductor, which means some black diamonds can conduct electricity.
How? Delocalized electrons can move freely between the layers of graphite inclusions within the gem. There are also gems that have piezoelectric properties, which allows them to conduct electricity. The most popular ones are quartz, tourmaline, and topaz.