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Moss agate (also called mocha stone) is a semi-precious gemstone formed from silicon dioxide. It is a form of chalcedony which includes minerals of a green colour embedded in the stone, forming filaments and other patterns suggestive of moss.〔(【引用サイトリンク】title=Moss Agate )〕 The field is a clear or milky-white quartz, and the included minerals are mainly oxides of manganese or iron. It is not a true form of agate, as it lacks agate's defining feature of concentric banding. Moss agate is of the white variety with green inclusions that resemble moss. It occurs in many locations. The colors are formed due to trace amounts of metal present as an impurity, such as chrome or iron. The metals can make different colors depending on their valence (oxidation state). Despite its name, moss agate does not contain organic matter and is usually formed from weathered volcanic rocks. Montana moss agate is found in the alluvial gravels of the Yellowstone River and its tributaries between Sidney and Billings, Montana. It was originally formed in the Yellowstone National Park area of Wyoming as a result of volcanic activity. In Montana moss agate the red color is the result of iron oxide and the black color is the result of manganese oxide. File:Austrian - Gothic-Style Bracelet - Walters 571999.jpg|Gothic-Style Bracelet; gold, carnelian, malachite, moss agate, amethysts, aquamarines, rubies. The Walters Art Museum. == References == 〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Moss agate」の詳細全文を読む スポンサード リンク
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