a. The ratio of the radius of the smaller ion to that of the larger ion.
It may not exceed 1. Hurlbut
b. The ratio of the radius of the smaller ion to that of the larger;
commonly cation to anion. Radius ratios are used to predict coordination
numbers of anions about cations in ionic crystal structures.
CF: Pauling's rules
Source:
Dictionary of Mining, Mineral, and Related Terms
