File:Lamproite (Middle Park Lamproite, Early Oligocene, 33 Ma; 5 to 5.5 km west of Lake Granby, northeast-central Grand County, northern Colorado, USA) 1 (14637155080).jpg
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Summary
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| Description |
Middle Park Lamproite from the Oligocene of Colorado, USA (10.5 cm across). Kimberlites and lamproites have tremendous economic importance because they are host rocks for gem-grade and industrial-grade diamonds. Kimberlites & 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. Kimberlites & lamproites 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. Here’s a rock from an unusual, small igneous body west of Lake Granby in northern Colorado. This is from the Middle Park Lamproite (= Rabbit Ears Lamproite, but it’s not from the Rabbit Ears Pass locality), an Early Oligocene intrusion (dike? sill? pipe?) having abundant, flow-aligned phenocrysts of phlogopite mica. The phlogopite (= glittery flakes) makes this a visually stunning rock (some appear bluish - that’s not real - it’s an artifact of scanner light reflectivity). Published literature indicates that the greenish-gray groundmass consists principally of analcime, biotite mica, richterite, apatite, ilmenite, and some diopside pyroxene. The Middle Park Lamproite is not known to be diamondiferous. Age: early Early Oligocene, 33 Ma Location: 5 to 5.5 km west of Lake Granby (it’s not from Rabbit Ears Pass), northeast-central Grand County, northern Colorado, USA |
| Date | |
| Source | Lamproite (Middle Park Lamproite, Early Oligocene, 33 Ma; 5 to 5.5 km west of Lake Granby, northeast-central Grand County, northern Colorado, USA) 1 |
| 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@N05/14637155080 (archive). It was reviewed on 4 November 2019 by FlickreviewR 2 and was confirmed to be licensed under the terms of the cc-by-2.0. |
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| Date/Time | Thumbnail | Dimensions | User | Comment | |
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| current | 14:30, 4 November 2019 | | 1,174 × 1,003 (263 KB) | Ainz Ooal Gown (talk | contribs) | Transferred from Flickr via #flickr2commons |
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