Quoting Wikipedia in reference to the variance in ceramics for the degree of crystallinity and number of electrons in their iconic and covalent bonds:

With such a large range of possible options for the composition/structure of a ceramic (nearly all of the elements, nearly all types of bonding, and all levels of crystallinity), the breadth of the subject is vast, and identifiable attributes (hardness, toughness, electrical conductivity) are difficult to specify for the group as a whole