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A Needle in a Haystack: How are Diamonds Detected in Rocks?

Kimberlite, a peculiar igneous rock best known for containing diamonds, also contains ‎a variety of minerals with unique chemical compositions. About 6,400 kimberlite pipes ‎‎(vertical columns of rock that come discharging when breaking the Earth’s surface) ‎have been discovered worldwide, 30 of which were found to contain diamonds.‎



Indicator mineralogy is the best diagnostic tool for identifying diamond-bearing ‎kimberlite. Certain indicator minerals typically occur within diamondiferous ‎Kimberlites and are used as mineralogical tracers by prospectors, as they follow the ‎indicator trail back to the volcanic pipe which may contain diamonds.



These minerals ‎are rich in chromium or titanium elements which impart bright colors to the minerals. ‎The most common indicator minerals are chromium garnets, eclogitic garnets, orange ‎titanium-pyrope, red high-chromium spinels, dark chromite, bright green chromium-‎diopside, glassy green olivine, black picroilmenite and magnetite.



These minerals are ‎generally absent from most other igneous rocks, making them particularly useful as ‎indicators for Kimberlites.‎



In the past decade, technological advances have led to increased sophistication of ‎determining indicator mineral chemistry for all indicator minerals. ‎

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