GENERAL GEOLOGY

Detailed explanation-1: -Of the common silicate minerals, olivine normally crystallizes first, at between 1200° and 1300°C. 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.

Detailed explanation-2: -Minerals near the top of the diagram, such as olivine and anorthite (a type of plagioclase), crystallize at higher temperatures. Minerals near the bottom, such as quartz and muscovite, crystalize at lower temperatures.

Detailed explanation-3: -Rocks that form from magma or lava cooled from high temperatures tend to contain a lot of iron and magnesium but little silica. These rocks are called mafic and tend to be dominated by dark colored minerals such as amphibole and pyroxene.

Detailed explanation-4: -When we follow the branch on the left, we see that at very high temperatures, olivine is the first mineral to form. In other words, olivine minerals, which are high in iron and magnesium, tend to crystallize at very high temperatures.