File:Thunder Egg Agate (Priday Blue Bed, John Day Formation, Miocene; near Madras, Oregon, USA) 1 (32744937906).jpg

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Agate ("Thunder Egg") from the Tertiary of Oregon, 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.

"Thunder eggs" are agate-filled masses that fill former cavities in volcanic rocks (see Colburn, 2004 for more info.).

Stratigraphy: Priday Blue Bed, John Day Formation, Miocene

Locality: Richardson Ranch (Richardson's Rock Ranch), northeast of the town of Madras, Jefferson County, north-central Oregon, USA

Reference cited:

Colburn (2004) - The Formation of Thundereggs (Lithophysae). 493 pp. (<a href="http://www.cvmineralclub.org/MAIN/Pages/Members Articles/Jack Marcy/The Formation of Thundereggs-Revised 2004.pdf" rel="nofollow">www.cvmineralclub.org/MAIN/Pages/Members%20Articles/Jack%...</a>) (This long document may take a little while to load on your computer.)
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Source Thunder Egg Agate (Priday Blue Bed, John Day Formation, Miocene; near Madras, Oregon, USA) 1
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@N05/32744937906. 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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current07:13, 10 October 2019Thumbnail for version as of 07:13, 10 October 20193,020 × 2,992 (2.59 MB)Ser Amantio di Nicolao (talk | contribs)Transferred from Flickr via #flickr2commons

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