The name of mica clay mineral is used widely in mineralogy, petrology and geology, although the mineral has not been defined mineralogically. Mica clay mineralsappeared in the literature have many characteristics, and so that many names are given to the minerals as a species and/or group names. This seems to lead some mineraloglogical confusions in the mineral description. Nomenclature for the minerals has many difficulties mineralogically, because the minerals are formed easely from other minerals by alteration and easely change to other minerals in natural conditions.
Logical discussions for the definition and nomenclature of the minerals are imposible in this paper, but it seems to be better that the term is used as a general name for some mica minerals, which are possible to become a clay mineral, when they are a main constituent mineral of a clay. If not, they are merely a mica mineral, not a mica clay mineral. If the mineral is defined as this, the name of the mineral should be given on the basis of the nomenclature of minerals.
Mode of occurrence has been described in many ways. Though the mode of occurrence seems to show only the form of a mineral aggregation found in nature, the description should show the form of the mineral assemblage from the concept of the genesis.
