Olivine lamproite (Prairie Creek Lamproite, Early Cretaceous, ~106 Ma; Crater of Diamonds State Park, south of Murfreesboro, Arkansas, USA) : 無料・フリー素材/写真
Olivine lamproite (Prairie Creek Lamproite, Early Cretaceous, ~106 Ma; Crater of Diamonds State Park, south of Murfreesboro, Arkansas, USA) / James St. John
| ライセンス | クリエイティブ・コモンズ 表示 2.1 |
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| 説明 | Weathered olivine lamproite from the Cretaceous of Arkansas, USA. (~6.3 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. The earliest diamond localities were India and Brazil. Africa was later 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 only publicly-accessible diamond collecting site in America - Crater of Diamonds State Park, in Arkansas. At the site, diamondiferous lamproitic rocks of the Prairie Creek Lamproite are exposed (actually, it’s just a field of rocky dirt). Diamonds are found regularly by tourists. The Prairie Creek Lamproite is an ultramafic pipe that intruded Proterozoic-aged (Grenvillian) basement rocks. Prairie Creek rocks are Cretaceous in age and date to about 106 million years old.In this sample, the light-colored grains are deteriorated olivine crystals.Geologic unit: Prairie Creek Lamproite (Prairie Creek Pipe), mid-Albian Stage, late Early Cretaceous, ~106 MaLocality: Crater of Diamonds State Park, just south of the town of Murfreesboro, Pike County, southwestern Arkansas, USA (34° 01’ 55” to 34° 02’ 05” North latitude, 93° 40’ 18” to 93° 40’ 25” West longitude) |
| 撮影日 | 2014-08-03 21:37:48 |
| 撮影者 | James St. John |
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