Summary: In the south-eastern part of the Khetri copper belt, actinolite occurs in association with alteration assemblages resulting from the Fe-Mg metasomatism that accompanied sulphide mineralization, and more commonly with albite-bearing rocks formed by albitization of quartzites and schists near granitic rocks. Within the latter occur many coarse, massive, and unoriented aggregates of actinolite crystals, individuals being commonly more than 10 cm long. Locally fluorite-bearing veins oecur within granitic and albite-quartz rocks. The actinolite is pleochroic from pale pink to green; γ: [001] = 26°; γ = 1·642 ± 0·003; 2V_α = 80°. The composition of the analysed actinolite closely compares with those published in the literature excepting in (OH), which is low. The mineral assemblages, formed by metasomatic replacement of pre-existing rocks, are equivalent to those of albite-epidote-amphibolite facies. The metasomatic fluid was apparently rich in Ca, F (indicated by fluorite), and oxygen (indicated by magnetite, ilmenite, and hematite).