Radiometric dating of rocks
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.
Most scientists today believe that life has existed on the earth for billions of years.
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.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.This left branch is called a discontinuous reaction series because each mineral has a different crystalline structure.
Recall that olivine is composed of a single tetrahedra and that the other minerals in this sequence are composed of single chains, double chains, and sheet structures, respectively.
Ordinarily, these reactions are not complete so that various amounts of each of these minerals may exist at any given time.