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Quartzite (from (ドイツ語:Quarzit)〔(German Loan Words in English ). German.about.com (2010-06-22). Retrieved on 2011-06-05.〕) is a hard, non-foliated metamorphic rock which was originally pure quartz sandstone.〔Essentials of Geology, 3rd Edition, Stephen Marshak, p 182〕 Sandstone is converted into quartzite through heating and pressure usually related to tectonic compression within orogenic belts. Pure quartzite is usually white to grey, though quartzites often occur in various shades of pink and red due to varying amounts of iron oxide (Fe2O3). Other colors, such as yellow, green, blue and orange, are due to other mineral impurities. When sandstone is cemented to quartzite, the individual quartz grains recrystallize along with the former cementing material to form an interlocking mosaic of quartz crystals.〔 Most or all of the original texture and sedimentary structures of the sandstone are erased by the metamorphism.〔 The grainy, sandpaper-like surface becomes glassy in appearance.〔 Minor amounts of former cementing materials, iron oxide, silica, carbonate and clay, often migrate during recrystallization and metamorphosis. This causes streaks and lenses to form within the quartzite. Orthoquartzite is a very pure quartz sandstone composed of usually well-rounded quartz grains cemented by silica. Orthoquartzite is often 99% SiO2 with only very minor amounts of iron oxide and trace resistant minerals such as zircon, rutile and magnetite. Although few fossils are normally present, the original texture and sedimentary structures are preserved. The term is also traditionally used for quartz-cemented quartz arenites, and both usages are found in the literature. The typical distinction between the two (since each is a gradation into the other) is a metamorphic quartzite is so highly cemented, diagenetically altered, and metamorphosized so that it will fracture and break across grain boundaries, not around them. Quartzite is very resistant to chemical weathering and often forms ridges and resistant hilltops. The nearly pure silica content of the rock provides little for soil, therefore, the quartzite ridges are often bare or covered only with a very thin layer of soil and (if any) little vegetation. ==Uses== Because of its hardness and angular shape, crushed quartzite is often used as railway ballast.〔(Railroad Ballast )〕 Quartzite is a decorative stone and may be used to cover walls, as roofing tiles, as flooring, and stairsteps. Its use for countertops in kitchens is expanding rapidly. It is harder and more resistant to stains than granite. Crushed quartzite is sometimes used in road construction.〔 High purity quartzite is used to produce ferrosilicon, industrial silica sand, silicon and silicon carbide. During the Stone Age quartzite was used, in addition to flint, quartz, and other lithic raw materials, for making stone tools.〔(Raw material ). Stone Age Reference Collection, Institute for archeology, University of Oslo, Norway〕 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「Quartzite」の詳細全文を読む スポンサード リンク
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