What do we know about diamonds?

2024 Author: Seth Attwood | [email protected]. Last modified: 2023-12-16 15:55

Everyone knows that a large diamond costs a lot of money. Almost everything is the hardest natural substance. And we know something else and will be happy to share this knowledge.

Rough diamonds

1. Diamonds are formed in the earth's mantle at depths of the order of a couple of hundred kilometers. There is tremendous pressure and very high temperatures. If the diamond on the surface is heated to the same temperature, it will burn. After all, this is exactly the same carbon as in the stove, it's just that the atoms are arranged differently. And there is no free oxygen in the earth's mantle, which is why diamonds do not burn.

2. The carbon of which the diamonds are composed, it seems, should not be at such depths. It is a light element, it is widespread in the earth's crust, and deeper lies the fact that for billions of years after the formation of the planet, it managed to "drown" in its bowels.

Apparently, the point is subduction … The oceanic crust, consisting mainly of basalts, forms in the middle of the oceans, in the zones of the mid-oceanic ridges. From there, it "moves apart" in opposite directions. The edge of the crust resting against the continent bends under it and gradually sinks in the mantle material.

Together with sedimentary rocks, which are rich in carbon. This process goes on at a rate of the order of centimeters per year, but continuously.

Blue diamond ring

3. Appreciated by jewelers and their customers, blue diamonds are almost ordinary diamonds colored with a small admixture of boron. Boron is even lighter than carbon and its presence at great depths is even less likely.

Apparently, it gets there in the same way, but in smaller quantities. Blue diamonds are being formed at a record depth of 600-700 kilometers. Therefore, they are very rare on the surface - about 0.02% of world production.

Rough diamond with inclusions of other minerals

4. During the crystallization of a diamond, substances surrounding it sometimes appear inside it. This is trouble for the jeweler and happiness for the geologist. The fact is that the crystal lattice of a diamond, due to its strength, can hold the captured minerals at the same pressure at which they were at the moment of the formation of our "stone".

And this is important, since many substances, as the pressure changes, pass from one state to another. For example, stishovite, which is stable at six or more gigapascals, transforms into coesite with decreasing pressure, and when it reaches the surface, into quartz, which is well known to us.

In this case, its chemical formula, of course, does not change - it is silicon dioxide, SiO₂… In addition, the pressure in the inclusions can accurately determine the depth of diamond formation.

Exhausted tube "Big Hole". Kimberley, South Africa

5. Diamonds reach the surface from kimberlite- ancient magma that once broke through to the surface through a kimberlite pipe - a relatively narrow, slightly widening vent towards the top. The name of the pipe and the mineral is due to the South African city of Kimberley, near which the first such pipe was discovered in the 19th century.

There are now approximately 1,500 pipes known around the world. Alas, diamonds are not found in all, but in about every tenth. Geologists believe that kimberlite accounts for about 90% of the world's diamond reserves.

Lamproite

6. The remaining 10% are confined to lamproites. They are also igneous rocks with high potassium and magnesium content.

Orange River, South Africa, today

7. Before the discovery of kimberlite pipes, diamonds were mined in placers, mainly river ones. As it is now clear, they were formed during the erosion of kimberlite volcanoes, of which only pipes have remained to this day. There were few placers of industrial importance in the world.

The Brazilian ones were practically exhausted by the end of the 18th century, the Indian ones a couple of centuries earlier. Debris in South Africa was found in the 19th century and it was their development near Kimberley that ultimately led to the discovery of the first pipe.