Bowen’s Reaction Series explains how minerals crystallize in cooling magma. It is a diagram which explains why certain minerals are found together very frequently while other minerals are hardly ever found together (which is very helpful!). There are two branches (the continuous branch and discontinuous branch) which meet in the middle and form a Y-shape.
On the continuous branch: there exists mafic calcium-rich plagioclase feldspar as well as intermediate sodium-rich plagioclase feldspar. The calcium-rich plagioclase feldspar breaks down uninterrupted by chemical reactions.
On the discontinuous branch: there exists mafic olivine and pyroxene as well as intermediate amphibole (hornblende) and biotite. The magma composition changes as chemical reactions occur between each location of this branch, thereby forming new minerals at each point. Essentially, some magma precipitates out and forms the different minerals.
These two branches meet at the bottom where the felsic minerals potassium feldspar, muscovite mica, and quartz are formed.
What’s the big deal about being mafic, intermediate, and felsic?
Mafic: high in magnesium content, less viscous, darker in color
Intermediate: a mix or in-between point with both mafic and felsic rocks present
Felsic: high in silica content, more viscous, lighter in color
When someone is looking for different types of rock (or different minerals) the Bowen’s Reaction Series is a great way to lead the way with trying to find out the best places to look for specific rocks and minerals. Granite, for example, is a very common felsic igneous rock which is prevalent throughout much of the mountains in North Carolina. Quartz, mica, and feldspars are all very common compositional minerals for granite rocks. Therefore, it makes sense that all of these minerals would be felsic because they are found in felsic granite. This is more significant and practical when someone first decides “I am going to try to find some _________ in North Carolina” (or elsewhere) on a rock-hunting trip. One of the best ways to find specific minerals (and the gemstones which can come from so many minerals) is to know where to be searching for these based on the Bowen’s Reaction Series. It would not be a good idea to search for olivine (where peridot can come from) in granite, for example, because it is very unlikely to find this mafic mineral in felsic rock. It is easy to do some research about the best types of rocks to find specific minerals in by reading online or in the plethora of mineralogy books available.
Higher temperature minerals and rocks (which are more mafic) are often the ones which weather and erode away the quickest. This is because the surface of the earth is so much cooler now than when these minerals and rocks were forming. Lower temperature minerals and rocks (which are more felsic) are the ones which we see more of today because they take longer to erode because of how the conditions at earth’s surface are similar to the conditions in which these rocks and minerals formed. The earth’s crust is mostly felsic. The earth’s mantle is mostly mafic. There is so much more which could be said about this, but after I learned more about Bowen’s Reaction Series I definitely had a greater appreciation for igneous rocks. Minerals are still my favorite (compared to rocks) because so many of them can be breathtakingly beautiful to me. The majority of igneous rocks are varying shades of black and gray (which are less than awe-inspiring for me), but now I see the bigger picture of how these igneous rocks can point me toward my favorite minerals that I seem to constantly be looking for whenever I am outside exploring and hiking.
Amy's Exploration of NC Geology 