Manuel de formation en valorisation de diamant

Diamonds are composed of carbon atoms that are bonded together in a unique and extremely strong way, making them the hardest substance on Earth. This unique bonding is a result of the extreme conditions of temperature and pressure that exist deep within the Earth's crust. The conditions necessary for diamond formation are precise and require a combination of high temperature and pressure, as well as a rich source of carbon. Diamonds are formed in two types of igneous rocks: peridotite and eclogite. Each of these rocks exists in specific conditions of temperature and pressure at specific depths within the Earth, and each provides its own source of carbon and releases it in different ways. It is believed that each of these rocks produces diamonds with different characteristics, crystal forms, and inclusions. Peridotite is the primary location where most diamonds are formed. It is an ancient type of rock that has been present since the Earth's formation and contains certain minerals that indicate the possible presence of diamonds. The peridotite contains carbon that is released as it melts under the Earth's internal heat. The abundance of available material means that the process of releasing carbon is relatively constant, indicating that diamond formation could be occurring currently. Eclogite, on the other hand, contains the remains of ancient plants and animals that provide the carbon for diamond formation. Eclogite is younger than peridotite and its carbon comes from organic matter such as ancient plants and animals that lived after the Earth's formation. These plants and animals became part of the eclogite, and their carbon is released when the rocks of the Earth's crust that contain them are subducted deep into the Earth. Diamonds are transported to the Earth's surface through two types of rocks: kimberlite and lamproite. However, diamonds are not formed in kimberlite and lamproite, but rather in peridotite and eclogite. Kimberlite and lamproite transport only a few diamonds to the surface. The heat trapped within the Earth maintains portions of the mantle in a molten state, forming magma. The heated magma rises, similar to hot air rising in a room. If the chemical composition is correct, the magma will form either kimberlite or lamproite. As the kimberlite or lamproite rises, it may encounter a pre-existing deep fracture in the crust and continue to move upward. If the kimberlite or lamproite passes through a diamond-bearing rock, it will pick up and transport diamonds that have already formed. As the kimberlite rises to the surface, the pressure above it decreases, and the magma gains speed with the decrease in pressure. The combination of speed and gas expansion is powerful enough to force the rising rock mixture to explode through the surface, creating a deep, carrot-shaped formation called a pipe. The expansion of gases and the speed of delivery are crucial for the survival of diamonds. The combination prevents diamonds from converting to graphite, which would occur if they were exposed to high temperatures with decreasing pressure over a long period. Kimberlite or lamproite do not erupt from the pipe like lava from a volcano; instead, they solidify within the pipe, trapping the diamonds inside.