In most gneisses, equi-dimensional mineral grains of quartz and feldspar are more abundant than the platy micas. Some of the textbooks in lab have more complete descriptions of metamorphic rocks. Boundaries between most of these textural categories are fuzzy. Study the metamorphic rocks on display and familiarize yourself with some of the varieties of foliated and non-foliated metamorphic rocks. Sedimentary rocks may be classified in a number of ways, and there is no general agreement or a single best classification.
Most systems rely on the mineralogy of the particles or clasts.
These rocks may also contain fossils, but mineral grains form the major part of these rocks. Limestone is the most common type of carbonate rock. The chief mineral component is calcite, CaCO3, which is readily identified because it reacts vigorously with weak hydrochloric acid. Look at the display of limestones to see how variable they are. Limestone textures will differ according to the relative amounts of large skeletal particles, fine carbonate mud, and clear calcite cement present.