基(ji)性的噴出巖。主要礦物成分為(wei)輝石(shi)和基(ji)性斜(xie)長(chang)石(shi),次要礦物為(wei)橄(gan)欖石(shi)、角閃石(shi)。多呈灰黑(hei)色(se)(se)或(huo)黑(hei)色(se)(se),常見有斑(ban)狀結構,斑(ban)晶為(wei)橄(gan)欖石(shi),輝石(shi)和基(ji)性斜(xie)長(chang)石(shi),基(ji)質(zhi)為(wei)隱晶質(zhi)或(huo)半晶質(zhi),由微晶或(huo)玻璃質(zhi)組成,基(ji)質(zhi)又有輝綠結構、粗玄結構、間隱結構、拉斑(ban)玄武結構和玻璃結構等,基(ji)質(zhi)中基(ji)性斜(xie)長(chang)石(shi)較多,也(ye)有部分暗(an)色(se)(se)礦物。
往往具有(you)氣孔狀(zhuang)構(gou)(gou)造、杏仁狀(zhuang)構(gou)(gou)造,有(you)時(shi)柱狀(zhuang)節理發(fa)育。根據次要(yao)礦物成分(fen)可分(fen)為(wei)橄欖玄(xuan)武(wu)巖、紫蘇(su)輝石玄(xuan)武(wu)巖、磁(ci)鐵玄(xuan)武(wu)巖等(deng)。按結構(gou)(gou)可分(fen)為(wei)粗玄(xuan)巖、細粒(li)玄(xuan)武(wu)巖、拉斑玄(xuan)武(wu)巖等(deng)。
按構造可以分為(wei)氣孔狀玄武(wu)巖(yan)(yan)(yan)、杏仁狀玄武(wu)巖(yan)(yan)(yan)、熔渣狀玄武(wu)巖(yan)(yan)(yan)和致密狀玄武(wu)巖(yan)(yan)(yan)等。如(ru)含10%以上(shang)的鉀長石(shi)(shi)稱(cheng)為(wei)堿性(xing)玄武(wu)巖(yan)(yan)(yan),如(ru)部(bu)或(huo)大(da)部(bu)由玻璃質組成(cheng)(cheng)稱(cheng)為(wei)玄武(wu)玻璃。玄武(wu)巖(yan)(yan)(yan)是火山巖(yan)(yan)(yan)中(zhong)分布廣的一(yi)種巖(yan)(yan)(yan)石(shi)(shi),常(chang)形成(cheng)(cheng)大(da)面(mian)積的熔巖(yan)(yan)(yan)臺地(di)。玄武(wu)巖(yan)(yan)(yan)除用作耐酸(suan)鑄(zhu)石(shi)(shi)原料外,其氣孔中(zhong)往往充填有(you)銅、鈷、硫磺、冰洲石(shi)(shi)等有(you)用礦產。
一種深成酸性火成巖。俗稱花崗石。二氧化硅含量多在70%以上。顏色較淺,以灰白色、肉紅色者較常見。主要由石英、長石和少量黑云母等(deng)暗(an)色礦物(wu)組成。石(shi)英含量(liang)為20%~40%,堿(jian)性長(chang)石(shi)多于斜長(chang)石(shi),約占長(chang)石(shi)總量(liang)的2/3以上。堿(jian)性長(chang)石(shi)為各種鉀(jia)長(chang)石(shi)和鈉長(chang)石(shi),斜長(chang)石(shi)主要為鈉更長(chang)石(shi)或更長(chang)石(shi)。暗(an)色礦物(wu)以黑云母為主,含少量(liang)角閃石(shi)。
具花(hua)(hua)(hua)(hua)崗(gang)(gang)(gang)結(jie)構或似斑狀(zhuang)結(jie)構。按所(suo)含(han)(han)礦(kuang)物(wu)(wu)種(zhong)類(lei),可(ke)分為(wei)(wei)黑云(yun)(yun)(yun)母花(hua)(hua)(hua)(hua)崗(gang)(gang)(gang)巖(yan)(yan)(yan)(yan)(yan)、白云(yun)(yun)(yun)母花(hua)(hua)(hua)(hua)崗(gang)(gang)(gang)巖(yan)(yan)(yan)(yan)(yan)、角閃花(hua)(hua)(hua)(hua)崗(gang)(gang)(gang)巖(yan)(yan)(yan)(yan)(yan)、二云(yun)(yun)(yun)母花(hua)(hua)(hua)(hua)崗(gang)(gang)(gang)巖(yan)(yan)(yan)(yan)(yan)等(deng)。按結(jie)構構造(zao),可(ke)分為(wei)(wei)細粒(li)花(hua)(hua)(hua)(hua)崗(gang)(gang)(gang)巖(yan)(yan)(yan)(yan)(yan)、中粒(li)花(hua)(hua)(hua)(hua)崗(gang)(gang)(gang)巖(yan)(yan)(yan)(yan)(yan)、粗粒(li)花(hua)(hua)(hua)(hua)崗(gang)(gang)(gang)巖(yan)(yan)(yan)(yan)(yan)、斑狀(zhuang)花(hua)(hua)(hua)(hua)崗(gang)(gang)(gang)巖(yan)(yan)(yan)(yan)(yan)、似斑狀(zhuang)花(hua)(hua)(hua)(hua)崗(gang)(gang)(gang)巖(yan)(yan)(yan)(yan)(yan)、晶洞花(hua)(hua)(hua)(hua)崗(gang)(gang)(gang)巖(yan)(yan)(yan)(yan)(yan)及(ji)片麻狀(zhuang)花(hua)(hua)(hua)(hua)崗(gang)(gang)(gang)巖(yan)(yan)(yan)(yan)(yan)等(deng)。按所(suo)含(han)(han)副礦(kuang)物(wu)(wu),可(ke)分為(wei)(wei)含(han)(han)錫石花(hua)(hua)(hua)(hua)崗(gang)(gang)(gang)巖(yan)(yan)(yan)(yan)(yan)、含(han)(han)鈮鐵礦(kuang)花(hua)(hua)(hua)(hua)崗(gang)(gang)(gang)巖(yan)(yan)(yan)(yan)(yan)、含(han)(han)鈹花(hua)(hua)(hua)(hua)崗(gang)(gang)(gang)巖(yan)(yan)(yan)(yan)(yan)、鋰云(yun)(yun)(yun)母花(hua)(hua)(hua)(hua)崗(gang)(gang)(gang)巖(yan)(yan)(yan)(yan)(yan)、電(dian)氣石花(hua)(hua)(hua)(hua)崗(gang)(gang)(gang)巖(yan)(yan)(yan)(yan)(yan)等(deng)。常見長石化、云(yun)(yun)(yun)英(ying)巖(yan)(yan)(yan)(yan)(yan)化、電(dian)氣石化等(deng)自(zi)變質作用。
花崗巖是一種分布廣泛的巖石,各個地質時代都有產出。形態多為巖基、巖株、巖鐘等。在成因方面,有人認為花崗巖是地殼深處的花崗巖漿經冷凝結晶或由玄武巖漿結晶分異而成,也有人認為是深度變質和交代作用所引起的花崗巖化作用的結果。許多有色金屬礦產如銅、鉛、鋅、鎢、錫、鉍、鉬等,貴金屬如金、銀等,稀有金屬如鈮、鉭、鈹等,放射性元素如鈾、釷等,都與花崗巖有關。花崗巖結構均勻,質地堅硬,顏色美觀,是建筑石料。