They are all derived from magma types that erupt rapidly from small amounts of melt, are rich in volatiles and magnesium oxide, and are less oxidizing than more common mantle melts such as basalt. These characteristics allow the melts to carry diamonds to the surface before they dissolve. Asked by the panel discussion moderator about the path forward for the KP, Mr. Asscher spoke about the introduction of Seven Principles in support of responsible sourcing at the KP. Deep mantle-derived rocks such as kimberlites, lamprophyres, and others. With decreasing pressure, the diamonds dissolve back into the rock.
In any case, kimberlites are often covered with vegetation, sediments, soils or lakes. In modern searches, geophysical methods such as aeromagnetic surveys, electrical resistivity and gravimetry, help identify promising regions to explore. This is aided by isotopic dating and modeling of the geological history. Then surveyors must go to the area and collect samples, looking for kimberlite fragments or indicator minerals.
To occur and survive in a metastable state at the surface they must arrive from depth quickly and very often crystals show dissolution features because the transport to the surface is not quick enough. It is the hardest naturally occurring substance known; it is also the most popular gemstone.
The gemological and industrial uses of diamond have created a large demand for rough stones. This demand has been satisfied in large part by synthetic diamonds, which have been manufactured by various processes for more than half a century. However, in recent years it has become possible to produce gem-quality synthetic diamonds of significant size.
It is possible to make colorless synthetic gemstones that, on a molecular level, are identical to natural stones and so visually similar that only a gemologist with special equipment can tell the difference. Roughly 49% of diamonds originate from Central and Southern Africa, although significant sources of the mineral have been discovered in Canada, India, Russia, Brazil, and Australia. They are mined from kimberlite and lamproite volcanic pipes, which can bring diamond crystals, originating from deep within the Earth where high pressures and temperatures enable them to form, to the surface. The mining and distribution of natural diamonds are subjects of frequent controversy such as concerns over the sale of blood diamonds or conflict diamonds by African paramilitary groups.
Under high pressure and temperature, carbon-containing fluids dissolved various minerals and replaced them with diamonds. Much more recently , they were carried to the surface in volcanic eruptions and deposited in igneous rocks known as kimberlites and lamproites. Diamond is the hardest natural substance known. It is formed deep in the mantle and is only brought to the surface via kimberlite pipes, lamprophyres, eclogites and other rocks that originate deep within the mantle. It is also found in alluvial deposits, along with quartz, corundum, zircon and other minerals, derived from such rocks, and in certain meteorites. Synthetic diamonds are diamonds manufactured in a laboratory, as opposed to diamonds mined from the Earth.
The latter have compositions that reflect the conditions where diamonds form, such as extreme melt depletion or high pressures in eclogites. However, indicator minerals can be misleading; a better approach is geothermobarometry, where the compositions of minerals are analyzed as if they were in equilibrium with mantle minerals. All three of the diamond-bearing rocks lack certain minerals that are incompatible with diamond formation. In kimberlite, olivine is large and conspicuous, while lamproite has Ti-phlogopite and lamprophyre has biotite and amphibole.
Diamonds found in alluvial and glacial gravels must have been released by fluvial or glacial erosion of the kimberlite matrix and then redeposited in rivers or in glacial till. Most natural diamonds have ages between 1 billion and 3.5 billion years. Most were formed at depths between 150 and 250 kilometres in the Earth’s mantle, although a few have come from as deep as 800 kilometres .
The diamond supply chain is controlled by a limited number of powerful businesses, and is also highly concentrated in a small number of locations around the world. They weather quickly and tend to have lower topographic relief than surrounding rock. If they are visible in outcrops, the diamonds are never visible because they are so rare.
The kimberlite pipes form from intrusions of magma into the Earth’s crust and deliver diamonds and other rocks and minerals from the mantle. The pipes themselves are often less than 100 million years old. However, the diamonds they carry were formed 1 to 3.3 billion years ago at depths of more than about 75 miles .