Agate nodule ("Lake Superior Agate") (Jo Daviess County, Illinois, USA) 11 : 無料・フリー素材/写真
Agate nodule ("Lake Superior Agate") (Jo Daviess County, Illinois, USA) 11 / 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 | Agate ("Lake Superior Agate") found in Illinois, USA."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.The specimen seen here is "Lake Superior Agate", which is the state gemstone of Minnesota. It is a variety that occurs around Lake Superior in Minnesota and the Upper Peninsula of Michigan. The agate filled large vesicles (gas bubbles) in ~1.1 billion year old basalt lava flows of Minnesota's North Shore Volcanic Series and Michigan's Portage Lake Volcanic Series. The reddish-brown coloration seen in this agate sample is the result of iron oxide impurities in the chalcedony layers.This sample was actually found near Dubuque, Iowa - way south of Minnesota. Pleistocene glaciers and post-glaciation meltwater rivers transported some agates from the Lake Superior area to deposits along the Mississippi River.Locality: undisclosed site attributed to the Mississippi River in western Jo Daviess County, northwestern Illinois, USA |
| 撮影日 | 2017-05-06 11:09:41 |
| 撮影者 | James St. John |
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