File:Kimberlite (Premier Kimberlite Pipe, Mesoproterozoic, ~1.2 Ga; Premier Mine, near Cullinan, South Africa) 5.jpg
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English: Kimberlite from the Precambrian of South Africa (~4.75 centimeters across at its widest).
Kimberlites and lamproites have significant economic importance because they are host rocks for gem-grade and industrial-grade diamonds. Kimberlites and lamproites are unusual igneous bodies having overall pipe-shaped geometries. Their mode of formation is only moderately understood because they have not been observed forming. These rocks are known from scattered localities throughout the world - only some are significantly diamondiferous. Classic localities for diamonds are India and Brazil. Africa was also discovered to have many kimberlites and is world-famous for producing large numbers of diamonds. Other notable diamondiferous kimberlite-lamproite occurrences include Russia, China, northwestern Australia, and northwestern Canada. Kimberlites are named for the town of Kimberley, South Africa. Several kimberlite pipes occur in the Kimberley area. Kimberlites have a gently tapering-downward, pipe-shaped cross-section. Lamproites have a cross-section more closely resembling that of a martini glass. The rock seen here is from the Premier Kimberlite in South Africa. The largest gem-quality diamond ever found came from this unit. When found in 1905, the Cullinan Diamond measured 10.5 centimeters (4.25 inches) across at its widest (about the size of a fist), and weighed ~1.5 pounds. Uncut, the Cullinan was 3026 carats. The Cullinan was cut into 105 gemstones, the largest of which is the Great Star of Africa (530 carats), which is on display with the British Crown Jewels in the Tower of London. The Premier Kimberlite Pipe erupted about 1.2 billion years ago, during the Precambrian. The pipe's rocks are significantly diamondiferous. Published inclusion dating studies show that Premier diamonds fall out into three age groups: 1) ~1.2 billion year eclogitic diamonds (Mesoproterozoic) 2) ~1.9 billion year lherzolitic diamonds (Paleoproterozoic) 3) ~3.2 billion year diamonds (Mesoarchean) Geologic unit: Premier Kimberlite Pipe, Mesoproterozoic, ~1.2 Ga Locality: Premier Mine, near the town of Cullinan, ~30 kilometers northeast of Pretoria, northeastern South Africa |
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| Source | https://www.flickr.com/photos/47445767@N05/51435556549/ |
| Author | James St. John |
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This image was originally posted to Flickr by James St. John at https://flickr.com/photos/47445767@N05/51435556549. It was reviewed on 8 September 2021 by FlickreviewR 2 and was confirmed to be licensed under the terms of the cc-by-2.0. |
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| current | 14:28, 8 September 2021 | | 2,776 × 2,579 (4.67 MB) | Ser Amantio di Nicolao (talk | contribs) | Uploaded a work by James St. John from https://www.flickr.com/photos/47445767@N05/51435556549/ with UploadWizard |
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