Sphalerite shows limited isomorphism. Consider a colorless sphalerite having 33% S and 67% Zn. Then, in a black-coloured sphalerite, with a 15% Fe substitution, the ratio of atomic proportions of Zn to that of Fe is ...........
A clinopyroxene crystal in a basalt, measured to have a composition of \( \text{Mg}_{1.2} \text{Fe}_{0.4} \text{Ca}_{0.4} \text{Si}_2 \text{O}_6 \), will have an Mg-number (Mg) of............%. (In integer)