Mineralogy and Chemistry of Basalts

When basaltic lava is abruptly quenched, it solidifies to glass. When slowly cooled, it crystallizes, more or less completely, to an assemblage of minerals. We may speak of the mineralogy of basalts in terms of these minerals (modal composition), and of the chemistry of basalts both in terms of elements (or oxides) and the potential minerals that might form if the lava were slowly cooled (normative composition). The calculation of normative minerals is discussed below, but first we may consider the actual minerals found in well-crystallized basalts.