Visualizing Fractional Crystallization and Crystal Settling

Figure 5.6 The Palisade Sill in the Hudson River valley of New York is a classic example of fractional crystallization and crystal settling. In the basaltic intrusion, small crystals formed in the chill zone as the outer areas of the intrusion cooled more quickly than the interior.

Figure 5.6 The Palisade Sill in the Hudson River valley of New York is a classic example of fractional crystallization and crystal settling. In the basaltic intrusion, small crystals formed in the chill zone as the outer areas of the intrusion cooled more quickly than the interior.

Fractional Crystallization Geology
As magma in an intrusion begins to cool, crystals form and settle to the bottom. This layering of crystals is fractional crystallization.

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As is often the case with scientific inquiry, the discovery of Bowen's reaction series led to more questions. For example, if olivine converts to pyroxene during cooling, why is olivine found in rock? Geologists hypothesize that, under certain conditions, newly formed crystals are separated from magma, and the chemical reactions between the magma and the minerals stop. This can occur when crystals settle to the bottom of the magma body, and when liquid magma is squeezed from the crystal mush to form two distinct igneous bodies with different compositions. Figure 5.6 illustrates this process and the concept of fractional crystallization with an example from the Hudson River valley in New York. This is one way in which the magmas listed in Table 5.1 are formed.

As fractional crystallization continues and more magma is separated from the crystals, the magma becomes more concentrated in silica, aluminum, and potassium. This is why last two minerals to form are potassium feldspar and quartz. Potassium feldspar is one of the most common feldspars in Earth's crust. Quartz often occurs in veins, as shown in Figure 5.7, because it crystallizes while the last liquid portion of magma is squeezed into rock fractures.

Fractional Crystallization Geology

Figure 5.7 These quartz veins represent the last remnants of a magma body that cooled and crystallized.

Figure 5.7 These quartz veins represent the last remnants of a magma body that cooled and crystallized.

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Responses

  • cailyn
    How can fractional crystallization and crystal settling?
    8 years ago
  • laura
    Is crystal settling a type of fractional crystallization?
    8 years ago
  • yonatan
    What is crystal settling in geology?
    8 years ago
  • evie
    What is fractional crystallization in crystal settling of Geology?
    6 years ago

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