A relationship between the approximate iron content in chlorite and intensity data obtained by means of the x-ray diffractometer has been established. Twenty-nine chemically analysed chlorites whose compositions range from those of the iron-rich varieties to those of the magnesium-rich varieties were studied. The results show that the intensities of x-rays diffracted from even-ordered basal planes of chlorite are proportional to the number of heavy atoms (Fe + Mn + Cr) in the octahedral layers of the mineral. A ratio of these intensities, expressed by the term (I₀₀₂ + I₀₀₄)/I₀₀₃, was selected as a variable factor representing the intensity, and its relationship to the number of atoms in the octahedral layers of chlorite was derived.