The geologist N.L. Bowen found that minerals tend to form in specific sequences in igneous rocks, and these sequences could be assembled into a composite sequence. No igneous rock ever displays the whole sequence.
Igneous rocks display a slice across the sequence.
Basalt, for example, typically has olivine and calcium plagioclase forming first, followed by pyroxene and more sodium-rich plagioclase. In granite, sodium plagioclase and biotite typically form first, followed by muscovite, potassium feldspar, and last of all quartz. The sketch below turns the series on its side. It's actually a more realistic view since successive minerals often form simultaneously. How Calderas Form Calderas form when volcanoes collapse.