Why is diamond so hard even though it is basically graphite?

Shirley Bassey’s song goes, “Diamonds are forever, they are all I need to please me…” Diamond rings, diamond necklaces, and all sorts of diamond jewelry are the priciest of women’s accessories.

You might be thinking where you could find a Koh-I-Noor, the most expensive diamond in the world. It weighs a massive 105.6ct and is oval-shaped. It is believed to have been mined in the 1300s in India, yet there’s a controversy that Britain stole the stone that rightfully belongs to India. Whether it’s true or not, Britain acquired the stone in 1850. And in 1852, Prince Albert had it cut to 105.6ct from 186ct to increase its brilliance and sparkle. It is also known as Mountain of Light and the Diamond of Babur. It is a colorless oval-cut diamond. (click here for more details)

What is a Diamond?

One of nature’s wonders is the formation of diamonds. It is a rare, naturally occurring mineral composed of carbon surrounded by four other carbon atoms connected by strong covalent bonds, which is known as the strongest type of chemical bond. Due to its composition and arrangement, it has become the most versatile and most durable natural substance known today.

Diamond is the best and most suitable cutting tool wherein high durability is needed. It is chemically resistant and has the highest thermal conductivity of any natural material. Diamond also possess optical properties such as a high index of refraction, high dispersion, and high luster. This makes diamond the world’s most popular gemstone and can be used in specialty lenses requiring performance and durability. (click here for more details)

How are diamonds formed?

Both graphite and diamonds are entirely created from carbon. But more recently discovered, made specifically of buckminsterfullerene, a discrete soccer-ball-shaped molecule containing carbon 60 atoms.

Atoms contain carbons that are sp3 hybridized or has tetrahedral geometry. Each carbon atom connects to four other carbon atoms having 1.544×10-10 meter distance apart, forming a C-C-C bond angle of 109.5 degrees. This sturdy, rigid three-dimensional structure results in an infinite network of atoms, which makes diamond the hardest, and most durable among other compounds. It also has a higher density than graphite.

Using the Mohs Hardness Scale, devised in 1812 by Friedrich Mohs, a German mineralogist, diamond is the hardest mineral. Ten minerals with a distinctly different hardness that ranged from a very soft mineral to a very hard mineral were elected and tested. Diamond is the best conductor of heat, conducting up to five times the amount that copper does. Also, it is a conductor of sound, but not electricity; it is an insulator, and its electrical resistance, optical transmissivity, and chemical inertness are correspondingly remarkable. (click here for more details)

There are artificial ways of producing diamonds. In as early as the 1950s, the General Electric and Industrial Distributors Ltd. company (later rebranded to Element Six) already started producing diamonds using the high-pressure, high-temperature process (HPHT). This condition mimics the environment 100 miles below the Earth’s surface. It grows diamonds using a source of carbon (typically graphite), and a metal that acts as a solvent for the carbon.

Another method is Chemical Vapor Deposition (CVD). This creates a diamond crystal in a layer-by-layer process with pressure and temperature conditions that are wildly different from those used in HPHT. In CVD, the thermal disassociation of hydrogen combined with a gaseous source of carbon in plasma at a temperature above 2,000°C, growth conditions is created by. The growth rates and purity control in this method result in high-quality polycrystalline and single-crystal synthetic diamonds. (click here for more details)

If you have a diamond ring, you will notice that there seems to be a rainbow light reflection when the light hits it. It is because it can disperse the light that creates the unique brilliance. More excellent dispersion means a better spectrum of colors. As the light enters through the top, it is reflected within the inner parts of the diamond before being aimed back towards the top and out through the surface. Diamonds are tiny, complicated prisms that create a rainbow effect with the dispersion of light.

This is also one best way to test if you have a genuine or fake diamonds. From the inside, it sparkles gray and white (known as “brilliance”) while outside, rainbow colors are reflected onto other surfaces. This dispersion of light is known as “fire.” A fake diamond will have rainbow colors that you can see inside the diamond. This is where people have the misconception that real diamonds reflect rainbow colors. (click here for more details)