A very useful generalized
geology diagram developed by N.L.
Bowen in the early twentienth century, it shows the idealized temperatures at which various
silica minerals
crystallize out of a
magma.
Discontinuous Continuous
1400° C | Olivine \ / Calcium-Rich |
| Pyroxene \ / Plagioclase | Mafic
| Amphibole \ / Feldspar |
| Biotite \ / Sodium-rich |
| | Orthoclase |
| | Muscovite | Felsic
800° C | | Quartz |
The continuous branch shows the crystallization of plagioclase evolving from calcic to sodic feldspars. The discontinuous branch shows the successive crystallization of more mafic magmas. As these minerals crystallize, the crystals that do not settle out in fractional crystallization react with still-liquid magma to form the next mineral in the series.
It works in reverse, too, to show the order in which mineral crystals melt when a rock is slowly cooled.
Bowen's reaction series is useful for determining the temperature and environment at which a rock formed. Always an important thing to be able to calculate at a moment's notice.