Crystallization differentiation

Japanese: 結晶分化作用 - けっしょうぶんかさよう（英語表記）crystallization differentiation

As magma cools and solidifies, it produces magma and rocks (→ igneous rocks) with different chemical compositions than the original. The general order of magma crystallization was shown based on the reaction series proposed by Canadian experimental petrologist Norman L. Bowen. Magma that rises from the upper mantle or lower crust and accumulates in the magma chamber is a complex liquid in which various rock-forming minerals are molten. As the magma gradually cools, minerals that are easy to solidify crystallize and sink to the bottom of the magma chamber, and the composition of the residual magma (residual liquid) also changes. Most of the magma that was initially formed was basaltic magma with a high magnesium and iron content. As it cools, olivine and pyroxene, which are rich in magnesium and iron and have high density, and plagioclase (anorthite), which is rich in calcium, crystallize and solidify to become gabbro, and the residual magma liquid changes from basaltic to andesite, which contains a lot of silicon dioxide. As the magma cools further, amphibole as well as pyroxene and plagioclase crystallize and solidify to form diorite, and the remaining magma liquid changes from andesite to rhyolitic, which contains more silicon dioxide. As the rhyolitic magma cools, biotite and sodium-rich plagioclase (albite) crystallize, and as it cools further, potassium feldspar (orthoclase), muscovite, and quartz crystallize, and as it cools, it becomes granite. (→ Plutonic rocks)

Source: Encyclopaedia Britannica Concise Encyclopedia About Encyclopaedia Britannica Concise Encyclopedia Information

Japanese:

マグマの冷却・固結が進むにつれて，元とは異なる化学組成のマグマや岩石（→火成岩）が生じる作用。カナダ出身の実験岩石学者ノーマン・L.ボーエンが唱えた反応系列 reaction seriesに基づき，一般的なマグマの晶出順序が示された。上部マントルや地殻下部から上昇しマグマだまりにたまったマグマは，さまざまな造岩鉱物が溶融した複雑な液体である。マグマは徐々に冷却していく過程で固化しやすい鉱物から結晶化してマグマだまりの底に沈み，それに伴って残留マグマ（残液）の成分も変化する。最初にできたマグマの多くはマグネシウムや鉄の含有率が高い玄武岩質マグマで，これが冷えていく過程でまず，マグネシウムや鉄を多く含み密度の大きい橄欖石や輝石，さらにカルシウムに富む斜長石（灰長石）が晶出・固結して斑糲岩となり，マグマの残液は玄武岩質から二酸化ケイ素を多く含む安山岩質に変わる。さらに冷却化が進むと，輝石，斜長石のほかに角閃石も結晶化し冷え固まって閃緑岩となり，マグマの残液は安山岩質から二酸化ケイ素をより多く含んだ流紋岩質へと変化する。流紋岩質のマグマが冷えると，黒雲母やナトリウムに富んだ斜長石（曹長石），さらに冷えてカリ長石（正長石），白雲母，石英が結晶化し，冷えて花崗岩となる。（→深成岩）

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