The Saving brighter come from Arda, but stones capable of imprisoning the sunlight are not found in Middle-earth: we have diamonds! These precious stones not only attract the interest of the female ego, but they are also a treasure trove of chemists' secrets, physicists and geologists!

The diamond is a lattice of carbon in solid form, like that of graphite in pencils, which due to its shape manages to have an incredible shine and hardness.

But to become a precious gem, these atoms must have a specific conformation of the atomic orbitals and must undergo particular conditions of temperature and pressure.

There are two theories on the formation of diamonds. The first assumes that they are formed in lithospheric mantle to a depth between 40 and 250 km, at a temperature between 900 ° C and 1400 ° C, and pressures between 10 and 80 thousand atmospheres.

The other theory predicts that diamonds are formed from metamorphic rocks during the processes of subduction, or where one plate slides under another (think of the “fire belt” around the Pacific Ocean to get an idea of ​​a subduction zone). The formation would begin within the tectonic plate sinking into the Earth's mantle, starting from 600 ° C and for pressures higher than 3 gigapascal. There is also another source of diamonds: in the impact areas of the meteorites diamond microcrystals were found.

An interesting study published in Nature has recently hypothesized a new possible path for the formation of diamonds: the precious minerals may also have formed in the depths of the Earth thanks to a reaction between rock and water! When there are infiltrations of fluids (water under supercritical conditions, not the water we are used to seeing habitually) in hot rocks at high pressures, in particular pH conditions, there may be a precipitation of carbon and the formation of the precious stone.

But for to find diamonds are not excavated up to hundreds of miles deep: these were brought to the surface by particular very violent explosive eruptions that in the past pierced the crust of the ancient continents forming those diamond chimneys where the mines are today, especially in Canada, Southern Africa and Australia.

Another secret of the diamond is the metastabilità! Diamond is thermodynamically unstable, it should spontaneously turn into graphite, if this does not happen, it is because its tetrahedral-shaped crystal lattice is kinetically stable and prevents the translation of carbon atoms into atoms with sp2 hybrid orbitals. Furthermore, exactly like a piece of coal, diamond tends to react with oxygen in a combustion reaction: a diamond thrown into the fate mountain would turn into CO2.

Due to their chemical and physical characteristics, diamonds are among the hardest materials, so much so that they can only be cut with other diamonds or with newly developed synthetic materials. For their hardness, for their high conductivity and for a thousand other properties, these stones are widely used in the field technological and industrial.

But for scientists studying their crystal lattice and their formation, diamonds are much more: they are chests of knowledge in which the history and secrets of the depths of the Earth are contained. In fact, both other minerals and fluids are often trapped inside diamonds, which provide information on the composition of the earth's interior. Analyzing the inclusions, we can reconstruct both the chemism of the materials and the pressure and temperature conditions present at the time of the formation of the diamond that contains them.

So we can say that diamonds are not just women's beautiful shimmering friends, rather they are themselves a mine of knowledge, a sort of time capsule that shows us what the inside of the earth was like a few billion years ago.

Sources:

https://www.nature.com/articles/ncomms9702
http://www.elementsmagazine.org/toc/toc_v1n2.pdf
https://www.smithsonianmag.com/travel/german-town-contains-millions-diamonds-180961467/