A homogeneous megacryst of schorlomite was investigated to determine t
he valence states of Fe and Ti and the crystallographic sites occupied
by these elements. The chemical composition of the specimen was analy
zed by electron microprobe, wet-chemical analysis, FTIR, and INAA. The
results from X-ray absorption near-edge structure spectroscopy (XANES
) are consistent with exclusively Ti4+ occupying the octahedral site o
nly. The tetrahedral site is deficient in Si and the results of low-te
mperature Fe-57 Mossbauer spectroscopy indicate that the remainder of
the site is occupied by Fe3+ and substantial Fe2+. A spin-allowed inte
nsified crystal-held transition of Fe-[4](2+) is present in the near-i
nfrared spectrum. The optical absorption spectrum is dominated by an i
ntense band centered at 500 nm with a full width of 8000 cm(-1) at hal
f maximum peak height; this band is assigned to an Fe2+-Ti4+ intervale
nce charge transfer transition between Fe-[4](2+) and Ti-[6]. The cati
on site occupancies in this specimen of schorlomite can be expressed b
y the following formula: [GRAPHICS] t are evident when their atomic ar
rangements are projected down [001]. In that projection, the chains ex
ist in (100) planes, with two planes per unit cell. In monazite the pl
anes are offset by 2.2 Angstrom along [010], relative to those in xeno
time, in order to accommodate the larger light RE atoms. The shift of
the planes in monazite allows the RE atom in that phase to bond to an
additional O2' atom to complete the REO(9) polyhedron.