The fatal flaw with radioactive dating methods
Evidence of this type led them to look into the possibility that a single magma might produce rocks of varying mineral content. Bowen discovered that as magma cools in the laboratory, certain minerals crystallize first.A pioneering investigation into the crystallization of magma was carried out by N. At successively lower temperature, other minerals begin to crystallize as shown in Figure 3.6.The following quote from The Earth: An Introduction to Physical Geology by Tarbuck & Lutgens, pp.55-57, (1987), gives us an idea of the tremendous complexity of the processes that occur when magma solidifies.Such a large variety of igneous rocks exists that it is logical to assume an equally large variety of magmas must also exist.However, geologists have found that various eruptive stages of the same volcano often extrude lavas exhibiting somewhat different mineral compositions, particularly if an extensive period of time separated the eruptions.Lava erupting earlier would come from the top of the magma chamber, and lava erupting later would come from lower down.
Further, the silicon content of the melt becomes enriched toward the latter stages of crystallization.
Bowen also demonstrated that if a mineral remained in the melt after it had crystallized, it would react with the remaining melt and produce the next mineral in the sequence shown in Figure 3.6.
For this reason, this arrangement of minerals became known as Bowen's reaction series.
The general idea is that many different minerals are formed, which differ from one another in composition, even though they come from the same magma.
The mineral makeup of an igneous rock is ultimately determined by the chemical composition of the magma from which it crystallized.
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During the last stage of crystallization, after most of the magma has solidified, the remaining melt will form the minerals quartz, muscovite mica, and potassium feldspar.