Xamarri is a small, airless, cratered terrestrial – a lifeless rock quite similar to Luna. Its frozen surface is mainly composed of silicates, though one hemisphere has several "seas" of dark basaltic rock.
The orbital distance here is a minimum derived from Kepler's equation, the cube root of constant 1.691 × 36.12. This constant is the solar mass 1.691 derived from the two outer planets, and assumes the orbit is not perturbed like the two inner planets. Given a slight perturbation its semi-major axis could be greater than 13.04 but if so, most likely negligibly.
However its surface albedo as calculated from parameters, including this distance, is −1.81. Mass Effect's description offers no offset for this impossibility. Based on Faringor's description (and the system's relative youth) there may be residual radioactivity in the planet's core.