Why Are Diamonds So Hard?

Diamonds are well known for their beauty and sparkle. But apart from their unique beauty, they are also well known for their strength. 

The word “diamond” comes from the Greek word Adamas which means unbreakable. It is one of the hardest materials found on the earth. But why are diamonds so hard? 

Diamond is an allotrope of carbon. The atomic arrangement of carbon atoms during the formation of diamond makes it as hard as it is. Diamonds are used in numerous industrial applications due to this property.

The hardness of a diamond is measured using Moh’s scale. Moh’s scale is rated from one to 10, where one denotes softest, and ten represents hardest. Diamonds are ranked ten on Moh’s scale. It is 40 times harder than corundum (rated nine on Moh’s scale), which is generally found in sapphires and rubies. 

However, the hardness of diamonds varies from one direction to the other. This makes it easier to cut and polish some of its faces as compared to others. Let us discuss more about the question: why are diamonds so hard? 

Why Are Diamonds So Hard?

Carbon has the capability of existing in different forms (called allotropes). Carbon can exist as carbon nanotubes, graphite, amorphous carbon, and diamond. All the allotropes consist of carbon but are different in their atomic arrangements, which gives rise to a unique structure and properties.

One of the most valued allotropes of carbon is diamond. Its hardness, high refractive index, and high dispersion of light make it useful in industrial applications like grinding, polishing, cutting, and others. Gemmologists use diamonds in making expensive jewelry that requires precision cutting.

Diamonds are formed when carbon deposits deep inside the earth’s surface (nearly 90-140 miles below the earth’s crust) are exposed to high temperatures and pressure. It brings the carbon atoms very close to each other.

The outer shell of the carbon atom has four valence electrons (valence electrons are relatively free electrons that can be shared between atoms). 

Tetrahedral Structure Forms Under High Pressure

Under high pressure and heat deep inside the earth’s crust, these four valence electrons share a bond with four other neighboring carbon atoms to form a strong covalent bond, resulting in a tetrahedral structure. 

Since the five carbon atoms are smushed together so close due to intense heat and pressure, the covalent bond formed is very tough to break. This is what makes diamonds so hard.

The arrangement of atoms is exceptionally rigid in diamonds, so very few impurities can contaminate it. Even then, while forming the covalent bond, some nitrogen atoms remain inside the tetrahedral crystal. This is what gives rise to a yellowish hue in some diamonds. 

Similarly, if few boron atoms are present in the diamond crystal, the diamond might have a bluish tint. Colored diamonds are extremely rare and more valuable than clear, white diamonds.

Diamond material is more durable compared to other materials like steel and others.

Moreover, the carbon atoms have no free electrons in their valence shell during diamond formation. So they are excellent heat conductors and have high thermal conductivity. It makes them useful in electronic parts like heat sinks.

But diamonds are also brittle. If you strike a diamond with a hammer, it can shatter into pieces.

Do Lab Diamonds Have the Same Harness as That of Natural Diamonds?

Lab diamonds are not naturally formed several miles below the earth’s crust. They are made in a sophisticated laboratory where the growth process is the same as the growth process of a natural diamond. So the color, cut quality, and clarity can be very similar to that of a natural diamond. 

However, the price of lab diamonds is lower compared to natural diamonds. Both natural and lab diamonds are composed of carbon. So they exhibit the same hardness as that of natural diamonds. In fact, both are rated a 10 on Moh’s scale.

How Can I Judge The Quality of a Diamond?

You can judge the quality of a diamond in four ways, listed below.

1. Color

The Gemological Institute of America (GIA) grades colorless diamonds from D to Z. the D grade denotes colorless, and the Z grade demotes diamonds with small tints of yellow. Know that a slight difference in color grade can impact the price of a diamond.

2. Cut

The cut of the diamond will have a high impact on its sparkle and brilliance. People usually think diamond-cut means the shape of a diamond-like round, princess cut, oval cut, and others. But diamond cut refers to how well the facets are cut so that they can interact with the light. Try to purchase a diamond with ‘good’ cut quality.

3. Clarity

Diamonds with high clarity grade have few or rare inclusions or impurities when seen under 10x power magnification.

4. Carat

Carat denotes the weight of the diamond that you intend to purchase. One carat of a diamond is equivalent to 0.2 grams (0.0071 oz).

A high carat diamond may not always be the better diamond. Other factors like cut quality, color grade, and clarity grade determine the overall quality of a diamond.

Related article: What Is a Certified Diamond: Certificates Explained

How Can I Care For My Diamond?

Diamonds are one of the hardest materials on the earth. But if you keep one diamond with another one, it can get damaged or get scratches. So you need to care for your diamond properly. Here are a few tips that may help you take proper care of your diamonds.

1. Properly Store Your Diamond

Proper storage of diamonds is essential. Try to store the diamond in a pouch consisting of soft cloth to avoid any scratches.

2. Inspect And Clean the Diamond From Time To Time

Diamonds can collect dust and dirt from time to time, hindering their sparkle and brilliance. So, you will want to occasionally take your precious and expensive diamonds to the professionals who can inspect and clean your diamond properly.

Related article: Is It Normal for Diamonds to Fall Out of Rings?

Wrapping Up

Diamonds are precious. Because of atomic arrangements, they are harder than typically rocks at normal pressure and temperature. But if you heat diamond to nearly 763 degrees Celsius, then it reacts with oxygen and forms carbon dioxide gas.

In this article, I’ve discussed the general chemical attributes of diamonds, as well as how they are valued on the market based on their traits. I hope this information will help you in buying and caring for your diamonds.

Related article:
Diamond Resale Value: How Much Is Your Diamond Worth?
Are Rubies Rarer Than Diamonds?