Figure 20. Close-up of the metamorphic rock shown in Figure 19. These layers were originally sedimentary rock - sandstone and siltstone - that have been converted by heat and pressure inside the earth into metamorphic rock. As metamorphic rocks, the mineral grains have been recrystallized into a microscopic texture somewhat like granite, so that the rock has been hardened. The sedimentary aspect is preserved, however, in the thin layers of different composition.
Last updated on September 3, 2008