![]() ![]() ![]() At that temperature, the plagioclase is calcium-rich (anorthite) (see Figure 2.15). As long as there is silica remaining and the rate of cooling is slow, this process continues down the discontinuous branch: olivine to pyroxene, pyroxene to amphibole, and (under the right conditions) amphibole to biotite.Īt about the point where pyroxene begins to crystallize, plagioclase feldspar also begins to crystallize. As the temperature drops, and assuming that some silica remains in the magma, the olivine crystals react (combine) with some of the silica in the magma (see Box 3.1) to form pyroxene. Of the common silicate minerals, olivine normally crystallizes first, at between 1200° and 1300☌. The sequence in which minerals crystallize from a magma is known as the Bowen reaction series (Figure 3.10 and Who was Bowen). This explains why a cooling magma can have some crystals within it and yet remain predominantly liquid. The minerals that make up igneous rocks crystallize at a range of different temperatures. ![]()
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