Coal is a combustible black or brownish-black sedimentary rock usually occurring in rock strata in layers or veins called coal beds or coal seams. The harder forms, such as anthracite coal, can be regarded as metamorphic rock because of later exposure to elevated temperature and pressure. Coal is composed primarily of carbon, along with variable quantities of other elements, chiefly hydrogen, sulfur, oxygen, and nitrogen. Coal is a fossil fuel that forms when dead plant matter is converted into peat, which in turn is converted into lignite, then sub-bituminous coal, after that bituminous coal, and lastly anthracite. This involves biological and geological processes. The geological processes take place over millions of years.
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110824048
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Mohaeljawphoto
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授權類型 | 尺寸 | 像素 | 格式 | 點數 | |
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標準授權 | L | 2454 x 2037 | JPG | 20 | |
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進階授權 | WEL | 4000 x 3320 | JPG | 88 | |
進階授權 | PEL | 4000 x 3320 | JPG | 88 | |
進階授權 | UEL | 4000 x 3320 | JPG | 88 |
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標準授權 | 480 x 398 px | JPG | 13 點 |
標準授權 | 800 x 664 px | JPG | 15 點 |
標準授權 | 1901 x 1577 px | JPG | 18 點 |
標準授權 | 2454 x 2037 px | JPG | 20 點 |
標準授權 | 3104 x 2576 px | JPG | 22 點 |
標準授權 | 4000 x 3320 px | JPG | 23 點 |
標準授權 | 5657 x 4695 px | TIF | 39 點 |
進階授權 | 4000 x 3320 px | JPG | 88 點 |
進階授權 | 4000 x 3320 px | JPG | 88 點 |
進階授權 | 4000 x 3320 px | JPG | 88 點 |