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This article is about the semi-precious stone. For other uses, see Agate (disambiguation). Agate is a microcrystalline variety of quartz (silica), chiefly chalcedony, characterised by its fineness of grain and brightness of color. Although agates may be found in various kinds of rock, they are classically associated with volcanic rocks but can be common in certain metamorphic rocks.[Donald W. Hyndman, David D. Alt (2002). Roadside Geology of Oregon, 18th, Missoula, Montana: Mountain Press Publishing Company, p. 286. ISBN 0-87842-063-0. ] Colorful agates and other chalcedonies were obtained over 3,000 years ago from the Achates River, now called Dirillo, in Sicily.[Agate Creek Agate. Retrieved on 2007-07-01.]
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North Dakota, USA
