Banded chalcedony (Prairie Agate) (White River Badlands area, western South Dakota, USA) 2 : 無料・フリー素材/写真
Banded chalcedony (Prairie Agate) (White River Badlands area, western South Dakota, USA) 2 / 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 | Banded chalcedony (agate) from South Dakota, USA (7.7 cm across at its widest)."Agate" is a rockhound/collector term for cavities in rocks (usually sedimentary rocks such as limestone or igneous rocks such as basalt) that have been partially or completely filled with irregularly concentric layers of microcrystalline, fibrous quartz (chalcedony - SiO2). Agate is quartz.This specimen is called "Prairie Agate". Macroscopically, it consists of banded chalcedony. Microscopically, bands and band sets have very irregularly concentrically layered chalcedony. This material may ultimately be derived from agate-filled cavities in Pennsylvanian-aged carbonate sedimentary rocks (limestones) to the west of its collection locality (western South Dakota). Erosion of the original rocks resulted in an agate clast. This specimen may have spent some time in an Oligocene conglomerate in the Chadron Formation. Agate clasts in Chadron Formation conglomerates were liberated by erosion, resulting in surface and near-surface, loose clasts.Locality: White River Badlands area, western South Dakota, USA |
| 撮影日 | 2014-11-01 19:53:15 |
| 撮影者 | James St. John |
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