Kimberlite

🔷Kimberlites, named after the town of Kimberly, South Africa, where they were first described, are volcanic rocks that originate in Earth’s mantle.
🔷They are mined exclusively for diamonds. The photo shows the “Big Hole” at Kimberly.
🔷The Hole was mined from 1871 to 1914 and reached a depth of 240 m below the surface. Subsequently it filled with water.

🔷Kimberlite eruptions are gas-powered explosive events. The magmas originate at depths of 150 to 450 km, deeper than other igneous rocks.
🔷 Most kimberlites are in small vertical columns called kimberlite pipes although some rare sills are known.

🔷 These pipes are the most important source of diamonds today. If kimberlite weathers and erodes, the diamonds may become concentrated in sedimentary deposits.

🔷Some kimberlites bring mantle xenoliths (pieces of mantle rock) to the surface; petrologists use these samples to study mantle chemistry and mineralogy.

🔷Kimberlites are ultramafic rocks, having high magnesium and low silicon contents, and are rich in potassium. Mg-rich olivine and carbonate minerals generally dominate, but some kimberlites contain significant amounts of phlogopite (Mg-rich biotite). Lesser amounts of serpentine, ilmenite, garnet, clinopyroxene, enstatite and chromite may be present. Most kimberlites are very old, having erupted between about 80 million and 2.5 billion years ago. A few younger ones, 10-20,000 years old, are in Tanzania and Democratic Republic of the Congo.