Basalt lava and Crust

Figure 4.00. Basalt lava. Lava breaking and flowing out from under a 3-cm-thick black, glassy crust of a pahoehoe flow from the Kilauea volcano on Hawaii. Click on the image for a larger version.

Binary Eutectic Diagrams

4.1 Overview

Equilibrium digrams for the melting and crystallization of igneous rocks have many similarities to saturation diagrams for ice-water-salt mixtures. The temperatures are higher, but molten silicate liquids can be saturated with minerals. This chapter introduces binary (two-component) equilibrium diagrams for simple igneous systems. Concepts that are developed include:
  • liquidus curves
  • eutectic points
  • congruent melting
  • incongruent melting
  • peritectic points
Concept that are used in this chapter, include chemical equilibrium, composition axes, saturation, saturation curves, and the the lever rule.