The fluorine micas (K-fluorine micas; KXMg3-XLiXSi4O10F2) having variable layer charges (x = 0.4-1.0) were synthesized. The lattice constant c decreased with a decrease in the layer charge while the lattice constants a and b increased. As the layer charge decreased, K-fluorine micas were changed into Na-fluorine micas more rapidly by NaB(C6H5)(4) treatment and were easier to cleave and change into the amorphous phase by grinding. The mica ceramics with lower layer charges showed lower electrical resistance than those with higher layer charges in the low-temperature region but higher electrical resistance in the high-temperature region. The results of the electrical resistance can be explained by the concentrations of the lattice vacancy and K+ ion in the interlayer. The dielectric loss tangent was influenced by the layer charge while the dielectric constant was almost unchanged. The chemical and physical properties of such micas are strongly dependent on the magnitude of the layer charge because the layer charge determines the interlayer bonding strength and the stability of mica structure. (c) 2005 Springer Science+ Business Media, Inc.