Diamond can form in Earth in a matter of hours - much faster than it takes for them to grow in a foundry.
For the most part, diamonds are then stuck in the ground for a long time until they are extracted. Diamond crystals can lie in the earth for a long time as does the most common of igneous rock.
All atoms on Earth are billions of years old. The water in the ocean is billions of years old. The atoms of our aboveground diamonds are billions of years old. Diamond miners have long claimed that their mined products are just as old. We now know that diamond can crystallize underground within hours and days under the kinds of pressures available deep inside the Earth.
Within the Earth’s mantle and under extreme conditions of heat and pressure, graphite is modified on an atomic level to form diamond. The atomic modification of minerals has to occur quickly – within days or hours – otherwise the atoms will not stabilize in order for the underground diamond to withstand.
How about Aboveground Diamonds?
Aboveground diamonds take billions of atoms to assemble quite magically just perfectly under the extreme temperature of a “sun on Earth” into the one and only arrangement that defines diamond.
Following similar principles, our aboveground diamonds consist of the same billion-year-old atoms, requiring extreme amounts of pressure and heat to form, just as those from the mines. Surprisingly it takes longer to form diamonds in our foundry than it does in the mantle. While diamond formation occurs within minutes to hours in the Earth, aboveground diamonds take weeks to form. Nevertheless, aboveground diamonds are available right there in the lab once formed, whereas underground diamonds require the long and destructive process of displacing millions of tons of the Earth’s surface to reach.