DISCUSSION
Compared to other gem occurrences in Sri Lanka, the
new deposit at Thammannawa has some characteris-
tic features. Whereas other deposits on the island con-
tain several gem varieties, only corundum has been
found at this new locality—mainly blue and a few yel-
low sapphires. Star varieties, geuda, and corundum of
other colors have not been found in this deposit. The
crystals possess a bright vitreous luster and good trans-
parency, with a glassy appearance; their sharp edges
and lack of alluvial transport are unusual for Sri
Lankan corundum. Also, their characteristically pure
blue color is different from the violetish blue typically
observed in sapphires from other parts of the country.
Some of the stones displayed color zoning, but none
showed the typical patches or concentrations of color
that are amenable to heat treatment.
Although an absorption line at 450 nm is weak to
moderate in typical Sri Lankan blue sapphires
(Hughes, 1997), a strong line was observed in the
Thammannawa specimens with both the prism and
diffraction-type spectroscopes. UV-Vis-NIR spectra of
Tham man nawa sapphires obtained by Pardieu et al.
(2012) confirmed the presence of this absorption line.