Let the radii of curvature of the concave surfaces be \( R \), and the refractive index of the material be \( 1.5 \). The separation between the images of \( O \) formed by each surface can be derived using the lens maker's formula for a spherical surface.
The distance between the two images is given by the formula:
\[
\text{Distance between images} = 2R \left( 0.6R + \frac{9}{7} R \right) = 0.114 R
\]
Thus, the separation between the images of \( O \) is \( 0.114R \).