Diamonds are considered one of the most famed and precious gemstones because of their unique visual appeal and properties. It has been used as an adornment and ornament across the globe for centuries but it is an expensive metal because of its rarity on Earth and hard mining procedures. It is also considered the hardest known substance and that property along with heat diffusibility makes it one of the finest cutting tools in industries as well.
Diamonds are quite old on the earth as studies show that their formation took place in the first couple of billion years of Earth as the Earth was hotter and conditions were more appropriate for diamond growth. The radioactive impurities such as potassium bounded with it can be used to date back diamonds as the pure diamond can’t be dated. This dating proves that most diamonds are millions of years and sometimes billions of years old.
Formation of Natural Diamonds
Diamonds are formed from carbon atoms bonded together in such a way that each carbon is bonded to four other carbon atoms to form a unique crystal lattice. Its strong covalent bonding with four neighboring carbon atoms is responsible for its hardness. These harsh conditions modified graphite’s hexagonal sheet patterns on the atomic level into the triangular shape of diamonds.
Some of the most common ways leading to the formation of natural diamonds are as follows
- Diamond Formation in the Mantle Zone
The carbon atoms involved in diamond formation are considered to have originated in Earth’s mantle. Carbon crystallization leading to diamond formation requires extreme temperature and pressure thus possible only in the core of Earth i.e., at least 150 – 200 kilometers or 100 miles below the crust. The temperature must be at least 1050 degrees Celsius and the pressure must be at least 45 – 60 kilo bars which are approximately 50,000 times the pressure of the earth’s surface. Thus all the natural diamond formed in earth needs such extreme temperature and pressure in the “diamond stability zones” and stored in these zones. This is the most common way of diamond formation and provides good quality diamonds.
- Diamond Formation in Subduction Zones
Subduction plates are found at the boundaries of convergent plates in a way that one plate is forced down into the mantle. The plate tectonics mechanism also known as “subduction” causes the transfer of carbon from earth surface as a part of carbonate sediments, shells, animals or plants to the Earth’s upper mantle and returned to the surface. Subducting plates are present at nearly 50 miles below the crust with a temperature of about 200 degrees Celsius. Research study shows subducted seawater is somehow also involved in the diamond formation.
Most diamonds formed by this process are small and not commercially valuable. Recently blue, boron-containing diamonds are supposed to be derived from subducted oceanic crust.
- Diamond Formation at Impact Sites
One of the origins of extreme temperature and pressure is the collisions of large asteroids on Earth. Thus, creating ideal conditions for diamond formation on these impact sites if an asteroid or meteorite falls on any carbon-containing rock. Such diamonds are rare and play no significant role in commercial diamond mining. Recently 13mm-sized diamonds were discovered at Popigal Crator in Russia.
- Diamond Formation in Space
Other than high temperature and pressure on Earth, diamonds can also be found due to a collision between an asteroid and Earth. The existence of diamonds in space is supported by many research theories and evidence from the meteorites hitting the Earth as a large number of nanodiamonds is detected in some fallen meteorites. It is suggested to be formed by high-speed collisions producing high temperature and pressure conditions ideal for diamond formation.
Other than meteorites, studies support the existence of diamonds on asteroids and planets as well like 55 Cancri e, Neptune and Uranus. Diamonds obtained from space are not of gem quality but can be used for different industrial processes due to their specific properties.
There is no certain evidence of how long it takes to form diamonds as some studies show that on change in conditions like carbon source, temperature and pressure, diamonds may sit for millions of years. So there is no particular evidence regarding the specific duration of diamond formation.
Transporting of Diamonds to the Earth surface
Naturally, diamonds are formed between 1 – 3 billion years and it needs volcanic eruptions to bring the diamonds to the surface of earth. It is considered a very violent eruption that must have occurred long ago in history. History research studies show that the earth was much hotter and so the volcanic eruptions were much deeper. The high levels of magnesium and carbon dioxide are responsible for the magma resulting in a volcanic eruption. In this process, not all the diamond’s structure can survive the process so it is one of the reasons for its rarity.
Other than volcanic eruption diamonds can be extracted by mining either open-pit or underground mining. Once crystallization is done it is suggested to rapidly transport the diamond to the surface to avoid any substantial changes. For that purpose, researchers use an elevator ride inside the volcanic pipe that can be either kimberlite or Lamproite when they contain adequate diamonds for profitable mining.
This kimberlite eruption is a very fast process as the slow process would ultimately convert the diamonds into graphite. It forms the bowl-shaped pockmark in the Earth after an eruption. According to one estimation traveling rate is 20 to 30 miles per hour in these kimberlite pipes. During mining, these kimberlite sites and other gemstones like garnet are also found. But sometimes the pipes don’t have enough diamonds that have no commercial interest.
Diamonds are mostly found all over the world but mostly not in valuable quantities. Commonly found in alluvial deposits along with other rocks and minerals. In many cases, diamonds are discovered far from the source. In the 1800s diamonds were discovered in volcanic pipes near South Africa that leads to the extensive research and searching of diamond reservoirs.
Types of Natural Diamonds
Although the main component of the diamond is carbon, there are always some impurities in it that are bonded when extracted and have to be removed during the refining process. It is mostly divided into two main types based on most prevalent impurities like nitrogen
- Type 1
This type has nitrogen as the main impurity commonly at a concentration of 0.1% that is sufficient enough to be detected by IR absorption spectroscopy. They are further divided into two types
It has nitrogen at a concentration of about 0.3% and accounts for 95% of all the natural diamonds. Its deposits are found in Cape Province in South Africa.
It has nitrogen impurities of 0.05% (not detectable by IR absorption spectrometry) and comprises 0.1% of all-natural diamonds.
- Type ll Diamonds
This type has no or very less nitrogen impurities that are not even detectable. It is further divided into two types
Type IIa Diamonds
They comprise almost 1-2% of all natural diamonds. They are colorless because of the absence of impurities.
Type IIb Diamonds
They are the rarest diamonds with low nitrogen but significant boron impurities. They comprise about 0.1% of all natural diamonds across the globe.
In 1954 scientists were able to create conditions needed to grow diamonds in the General Electric laboratory. Lab-grown diamonds are considered similar to real diamonds as they are made of carbon atoms under almost the same conditions. Mostly lab-grown diamonds are used for industrial purposes because of specific properties.
Formation of lab-grown diamonds:
Lab-grown diamonds are formed by placing a starter “seed” under extreme heat and pressure. In a sealed chamber, crystallization allows the artificial diamonds to mature and form molecular bonds while the sealed chamber mimics the growing process of natural diamonds. After the artificial diamonds form molecular bonds, they are then cut and polished by experts. They are also made in different colors by adding particular impurities in it like nitrogen imparts yellow color and boron imparts blue color.
The most common technique used in the creation of lab-grown diamonds is Chemical Vapour Deposition CVD i.e., the use of carbon-rich gases as carbon sources such as methane and HTHP (high-temperature high pressure) which uses high pressure and temperatures so that the graphite within the starter seed dissolves. All lab-grown diamonds require a high amount of electricity that can be produced by burning coal.
As its name shows diamond simulants have a resemblance to a real diamond but their physical, chemical, optical characteristics are different. These are often used in place of real diamonds. For example, Cubic zirconia is the most popular diamond stimulant used nowadays.
Diamonds are among the most precious gemstones because of their unique properties, luster and the way of its formation and mining procedures. It is considered one of the best gemstones for jewels and is also used in industries for cutting purposes. So its role in our lives is very significant that makes it special and valuable.