2. Bowen’s Reaction Series
Describes the formation of igneous rocks from different starting temperatures and magma compositions.
Fractional Crystallization – process by which minerals are formed and removed from the molten rock

3. Discontinuous Reaction Series
On left
Earlier-formed crystals react with the remaining magma in a series of steps to form a new mineral
Because the series of minerals is not dependent on one mineral depleting the magma of certain elements before another mineral can form, it is called discontinuous.

4. From an initial basaltic magma, the first formed mineral is olivine (Mg2SiO4).
removal of olivine increases the silica content and decreases the iron and magnesium in the parent magma
As temperatures lower, a new chain silicate mineral, pyroxene (CaMg(SiO3)2 is formed.

5. As temperatures drop further (1100C - 850C), the magma becomes even richer in silicates.
Amphibole begins to form
The original basaltic magma becomes andesitic magma

6. As temperatures cool to 800C and silica increases further, the sheet silicate biotite forms.
Andesitic magma now evolves into rhyolitic magma.

7. Quartz forms last at low temperatures.
Muscovite mica and potassium feldspar also form at this temperature
All of these minerals are poor in mafic components (Fe, Mg) which were removed from the melt by minerals that formed earlier.

8. Continuous Reaction Series
On right
Earlier formed minerals slowly and steadily change into new minerals
Crystallization of plagioclase feldspar depletes calcium from the parent magma and replaces the missing element with sodium as new minerals are formed
Feldspar minerals form continually at the same time as minerals shown opposite in the Discontinuous Series
Again, the series is continuous because the plagioclase is the same mineral group being formed with variations in Calcium and Sodium content.

10. Bowens and Weathering
Minerals that crystallize at high temperatures generally break down more quickly on the surface on Earth
Minerals that crystallize at low temperatures are more abundant on the surface because they are more resistant to weathering

11. Click for Hyperlink