  We have developed an algorithm (x2abundance) to derive the lunar surface
chemistry from X-ray fluorescence (XRF) data for the Chandrayaan-1 X-ray
Spectrometer (C1XS) experiment. The algorithm converts the observed XRF line
fluxes to elemental abundances with uncertainties. We validated the algorithm
in the laboratory using high Z elements (20 < Z < 30) published in Athiray et
al. (2013). In this paper, we complete the exercise of validation using samples
containing low Z elements, which are also analogous to the lunar surface
composition (ie., contains major elements between 11 < Z < 30). The paper
summarizes results from XRF experiments performed on Lunar simulant (JSC-1A)
and anorthosite using a synchrotron beam excitation. We also discuss results
from the validation of x2abundance using Monte Carlo simulation (GEANT4 XRF
simulation).
