Schist Schists are strongly foliated rocks with abundant platy and elongated minerals that can be readily split into thin flakes. The grains in a schist are coarser than in slate. Gneiss forms under high-grade metamorphism from granite or diorite and other rocks. Nonfoliated metamorphic rocks Not all metamorphic rocks have a foliated texture. Metamorphic rocks composed of only one mineral having equidimensional crystals usually are not visibly foliated.
Marble is a coarse, crystalline metamorphic rock composed almost entirely of calcite or dolomite.
Quartzite is a nonfoliated metamorphic rock formed from quartz sandstone. Engineering considerations of metamorphic rocks Foliated rocks possess prominent directional properties. The strength is much weaker in the direction of the foliation than in other directions. In tunnel construction, foliated metamorphic rocks are generally more costly because of more steel supports. The types of rocks we talked about can be transformed from one type to another.