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Glauconite

The Mica Minerals

Glauconite is a dark green mica with the formula (K,Na)(Fe3+,Al,Mg)2(Si,Al)4O10(OH)2. It forms by alteration of other micas in marine sedimentary rocks and is used by organic gardeners as a slow-release potassium fertilizer.
Makes marine rocks green
Photo courtesy Ron Schott of Flickr under Creative Commons license CC BY-NC-SA 2.0

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Gallery Index: The Mica Minerals

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