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File:Banded chalcedony (Prairie Agate) (White River Badlands area, western South Dakota, USA) 1 (15662979766).jpg

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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
Date
Source Banded chalcedony (Prairie Agate) (White River Badlands area, western South Dakota, USA) 1
Author James St. John

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This file is licensed under the Creative Commons Attribution 2.0 Generic license.
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This image was originally posted to Flickr by James St. John at https://flickr.com/photos/47445767@N05/15662979766 (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
current07:11, 10 October 2019Thumbnail for version as of 07:11, 10 October 20193,076 × 2,576 (3.1 MB)Ser Amantio di Nicolao (talk | contribs)Transferred from Flickr via #flickr2commons

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