File:Agate (Rio de Sol, Brazil) 2 (31941597703).jpg

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Agate and quartz lining a large, complex geode from Brazil. (Jerry Schaber collection)

This shows the interior of a highly complex geode. Geodes are small to large, subspherical to irregularly-shaped, crystal-lined cavities in rocks. They form when water enters a void in a host rock and precipitates crystals. The most common geode-lining mineral is quartz.

The thinly layered areas are agate. "Agate" is a rockhound/collector term for irregularly- & concentrically-layered masses of microcrystalline quartz. Individual layers consist of translucent or opaque, microcrystalline, fibrous quartz called chalcedony. Impurities in different layers cause variations in color. Many agate masses are simply geodes that have completely filled up with quartz. Common agate colors are clearish-whitish-grayish, brownish-red, and yellowish-brown. Commercial agates that occur in greens and blues and purples are almost always dyed (faked).

The glittery crystals near the center of each cavity are macrocrystalline quartz. The pustulose masses lining some of the cavities are mammiform chalcedony.
Date
Source Agate (Rio de Sol, Brazil) 2
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@N05/31941597703 (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
current07:12, 10 October 2019Thumbnail for version as of 07:12, 10 October 20192,341 × 1,998 (1.3 MB)Ser Amantio di Nicolao (talk | contribs)Transferred from Flickr via #flickr2commons

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