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File:Agate nodule ("Lake Superior Agate") (floor of Lake Superior, offshore Keweenaw Peninsula, Michigan USA) 6 (46703504835).jpg

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(~6.3 centimeters 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.

The above specimen is "Lake Superior Agate", which 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 various colors seen in this agate sample are the result of iron oxide impurities in the chalcedony layers.

Locality: attributed an offshore locality - the floor of Lake Superior, offshore from the western margin of northern Michigan's Keweenaw Peninsula, USA
Date
Source Agate nodule ("Lake Superior Agate") (floor of Lake Superior, offshore Keweenaw Peninsula, Michigan USA) 6
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@N05/46703504835 (archive). It was reviewed on 10 October 2019 by FlickreviewR 2 and was confirmed to be licensed under the terms of the cc-by-2.0.

10 October 2019

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Date/TimeThumbnailDimensionsUserComment
current07:15, 10 October 2019Thumbnail for version as of 07:15, 10 October 20192,502 × 1,981 (2.94 MB)Ser Amantio di Nicolao (talk | contribs)Transferred from Flickr via #flickr2commons

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