Why Are Diamonds Hard and Durable Over Time?

Diamonds are often favored for having the highest hardness among natural and synthetic gemstones. This helps diamonds remain durable over time and be used for a long time. Thanks to that, diamonds are considered a symbol of eternal love. However, few people know why diamonds are hard. Below are explanations for this issue.

Why are diamonds hard?

The formation of diamonds

Diamonds are considered the hardest material on Earth. Their name comes from Greek, meaning “unbreakable” or “invincible”. The hardness of diamonds gives them incredible cutting ability, along with perfect beauty.

The formation of diamonds has greatly influenced the reason why diamonds are hard. Each diamond we are using today was formed about 3.3 billion years ago. Older than the time when humans came to know the Earth.  Diamonds are created from carbon-containing minerals, under high temperature and pressure at a depth of 100km beneath the ground.

Diamonds are hard mainly because of their extremely harsh formation process

The pressure in this place is about 4905000000 kg and the temperature is about 12000. These are enormous figures, helping carbon crystallize more tightly. Each C atom is connected to 4 surrounding C atoms. Thanks to the compressive force at a very great depth, the crystal has a solid, durable structure and is difficult to break. Today, the hardness of diamonds is considered perfect, reaching 10h on the Mohs scale. The highest level among natural as well as synthetic stones.

In addition, thanks to their perfect hardness, diamonds are not only used for beauty, but are also added to tools such as knives, drills… to serve industry. Perfect hardness allows diamonds to cut and drill easily.

Why is graphite not as hard as diamond?

Many of you reading this may share the same question: Both are formed from carbon, but why are diamonds many times harder than graphite? The main reason is that in graphite, carbon atoms are arranged in layers and formed on top of one another. This makes the bonding forces between the atoms very small. Therefore, graphite layers are very easy to separate from each other.

Why is graphite not as hard as diamond?

In contrast, diamonds are also formed from carbon, but they possess a very high hardness. The reason is that diamonds are formed at a depth of 100 miles, where the temperature and pressure are very high. Carbon is buried in the deeper layers of the Earth's crust. Thanks to this, carbon is able to crystallize highly, creating a crystal with a very solid structure, so it has very high hardness.

Physical properties of diamonds

Color

The color of diamonds is truly very diverse: colorless, blue, green…. The more outstanding the color of a diamond, the greater its value.

The main cause of color is that during the stone's formation process, impurities are mixed in. In addition, nitrogen is also a major reason why diamonds have color. Almost all naturally sourced diamonds contain nitrogen. Therefore, stones that contain no nitrogen are truly very rare and may not exist.

Diamonds come in many diverse colors due to impurities during the formation process

Temperature resistance

At an atmospheric pressure of 1atm, diamonds will have properties similar to graphite and can decompose. Diamonds will burn at a temperature of about 8000°C under conditions with sufficient oxygen.

Under normal temperature and pressure, a diamond can turn into graphite after about 15 billion years. Approximately the same amount of time as the age of the universe up to now.

Optical properties

Diamonds have good dispersion because they possess a rapidly changing refractive index and light wavelength. This gives diamonds the ability to turn white light rays into colored light rays. This helps create the appeal of diamond jewelry. The refractive index of this gemstone is about 2.417, 1.5 times that of glass.

Electrical conductivity

Except for blue diamonds, all other types of diamonds have good electrical conductivity. The reason is that blue diamonds do not contain electrically conductive impurities.

Electrical conductivity of diamonds

Hopefully the sharing above helps you understand more about why diamonds are hard. The main reason is the extremely harsh formation process of diamonds, which makes them durable and solid.