I think I will blog now and then about rocks as opposed to minerals. Rocks are aggregates of minerals, classified according to how they were formed (igneous, sedimentary, metamorphic). These can be subdivided into other classifications, such as particle size. Formation of rocks is a gradual process and one type sort of morphs into another. Selecting reference points is arbitrary; however, it has been done and there are a finite number of rock types, according to petrologists. Usually in books, igneous rocks are considered first. The first one on that list is andesite, named for the Andes mountains. It is an intermediate crystalline rock, consisting mainly of plagioclase feldspar. There is also a mineral called andesite, which confuses matters.