File:Dacite obsidian-flint cross.jpg

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English: Artist: Mary Ellen St. John

The black-colored pieces are glassy dacite - essentially, a form of obsidian. Obsidian is a glassy-textured extrusive igneous rock. It is often rhyolitic in composition, but can be rhyodacitic or dacitic as well. The latter two are less silica-rich than rhyolite.

The light-colored pieces are flint, a cryptocrystalline, quartzose sedimentary rock - its geologic name is "chert". A famous occurrence of high-quality, colorful flint is Flint Ridge, Ohio. Prehistoric American Indians quarried this material to make arrowheads, spearpoints, and other tools. Flint is the "official state gemstone" of Ohio.
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Source https://www.flickr.com/photos/47445767@N05/51072296958/
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@N05/51072296958. It was reviewed on 27 March 2021 by FlickreviewR 2 and was confirmed to be licensed under the terms of the cc-by-2.0.

27 March 2021

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current06:08, 27 March 2021Thumbnail for version as of 06:08, 27 March 20212,491 × 3,514 (4.66 MB)Ser Amantio di Nicolao (talk | contribs)Uploaded a work by James St. John from https://www.flickr.com/photos/47445767@N05/51072296958/ with UploadWizard

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