The masonry is well-preserved and built from cut schistose slabs. Upland soils derive from granitic, schistose, or sandstone parent rocks more acidic and less fertile. The white powder in Thiruman is derived from decayed schistose mica. The rock of Beinn Sgritheall is of the schistose type. Greenschist often has a lepidoblastic, nematoblastic or schistose texture defined primarily by chlorite and actinolite. It occurs in marble and schistose rocks of metamorphic origin. The ancient schistose rocks are covered by the Deccan Traps (Cretaceous Eocene). It is typically dark-colored and dense, with a weakly foliated or schistose (flaky) structure. The schistose rocks are composed of biotite, chlorite, feldpsar, quartz, rare garnet.