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In geology felsic refers to igneous rocks that are relatively rich in elements that form feldspar and quartz.〔Marshak, Stephen, 2009, ''Essentials of Geology,'' W. W. Norton & Company, 3rd ed. ISBN 978-0393196566〕 It is contrasted with mafic rocks, which are relatively richer in magnesium and iron (ferric). It refers to those rocks rich in silicate minerals, magma, and rocks which are enriched in the lighter elements such as silicon, oxygen, aluminium, sodium, and potassium. They are usually light in color and have specific gravities less than 3. The most common felsic rock is granite. Common felsic minerals include quartz, muscovite, orthoclase, and the sodium-rich plagioclase feldspars. In terms of chemistry, felsic minerals and rocks are at the other end of the elemental spectrum from the mafic minerals and rocks. ==Terminology== In modern usage, the term ''acid rock'', although sometimes used as a synonym, refers to a high-silica-content (greater than 63% SiO2 by weight) volcanic rock, such as rhyolite. The term was used more broadly in older geologic literature. It is considered archaic now, as the terms "acidic" and "basic rock" were based on an incorrect idea, dating from the 19th century, that silicic acid was the chief form of silicon occurring in rocks. The term "felsic" combines the words "feldspar" and "silica". The similarity of the term ''felsic'' to the German words ''Fels'', meaning "rock", and ''felsig'', meaning "rocky", is purely accidental, as ''feldspar'' is a borrowing from German ''Feldspat'', which derives from German ''Feld'', meaning "field". 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「felsic」の詳細全文を読む スポンサード リンク
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