Why are there colored diamonds?

The pink diamond ‘Pink Star’ has just become the most expensive gemstone in the world.

What makes colored diamonds so popular?

Colored diamonds are a rarity. It is estimated that only 1% of natural diamonds have it. And only 1% of that 1% is roses. Hence they are so extremely valuable.

Pink Diamond facts and red diamonds acquire their color because at some point during the formation process they experience an “abrupt and localized” overpressure that alters normal packing in a given area, thus giving rise to a layer or strip that interacts with the light visible in a different way, absorbing part of it, which favors its coloration.

A diamond is one of the forms, variants or allotropes in which the chemical element carbon is presented. Specifically, diamonds are crystalline structures that form when, due to the enormous pressures and temperatures that occur in the interior of the planet, clusters of carbon atoms – on the order of many billions – are arranged and joined together forming a solidly packaged three-dimensional network that, subsequently, and due to geological processes, ends up reaching the earth’s crust – unless, of course, they are synthetic.

It is precisely it’s carbonic’ nature that justifies that most are transparent or translucent. Without going into big considerations, the electronic distribution of the carbon atom causes this crystalline structure to absorb nothing of the visible radiation – a more exhaustive explanation would require referring to band theory.

So perfect diamonds, or ideals, are transparent. The existence of some colored diamonds serves three factors:

The presence of impurities is traces or minimum amounts of other elements with characteristics similar to carbon and that replace a part of the atoms of this in the crystalline network. Structural defects or alterations caused during the diamond formation process. By natural irradiation from radioactive minerals at the site of diamond formation any of these factors cause a local alteration of the electronic distribution that leads to the absorption of a certain strip or region of the visible spectrum, subtracting it from white light and, therefore, it makes these diamonds present one color or another.

In the case of yellow diamonds, the most abundant within the colored ones, they appear due to the presence of nitrogen impurities. That is when a quantity – very small, but significant – of nitrogen atoms take the place of carbon in the crystalline structure.

While in blue diamond’s boron is the element that replaces carbon.

Green diamonds originate from the natural irradiation of neighboring rocks. Upon reaching the diamond, the radiation emitted by the rocks modifies the electronic distribution, giving rise to this tonality that, in addition, is usually concentrated in the outer layers of the stone, since the radiation is attenuated as it penetrates into it.

Of course, it is not about pure colors. Depending on whether there are more or fewer impurities; if the altered or defective areas are more or less abundant and more or less extensive; or if the irradiation is more or less powerful, the tone and intensity of the color of the diamond are affected. And, in the same way, it may be the case that two of these factors converge on the same diamond: for example, impurities of an element and structural defects. This is, in fact, what happens in violet and purple diamonds, which get their color by the combination of structural defects -rose- and the presence of boron -blue-. The sum of both colors produces a definitive violet tone.

And some of that also occurs in the much less priced gray or black diamonds, which are caused by the presence of graphite inclusions, which is another of the allotropic forms of carbon. That is to say, ‘grains’ where carbon has been grouped not as a three-dimensional network, but as sheets or layers. As can be understood as inclusions of “defective structures” and as everyone has in mind, graphite, unlike diamond, does have color, gray. Depending on the number of inclusions of this nature, the diamond can turn from gray to black.

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