Abstract: Chlorite minerals from six distinctive chlorite-quartz parageneses in central Borrowdale have been studied. All specimens were 14Å (IIb) chlorites. Cell parameters and β refractive index exhibit an approximate linear dependence on composition for the range Fe/(Fe + Mg) = 0.46 to 0.84. The data indicate an apparent trend that chlorite iron content increases with temperature. This is in conflict with experimental studies (Flemming and Fawcett, 1976), and it is inferred that the observed compositional variations reflect the availability of iron in the veins rather than a dependence on temperature.