is some variability in these needle or tube-like inclusions.
In this slide of 50x, you can see some "not so straight"
needles. the example shown in this slide are not common.
credit: Alan Hodgkinson, FGA, DGA Oct,1998
photo, taken at 10x, shows moissanite's double refraction. Moissanite
is cut with the table perpendicular to the "c" axis;
consequently, by looking through the table of a stone, one is
viewing the singly refractive direction which does not produce
doubling. For viewing the double refraction through the crown
or pavilion facets is recommended. Diamond is singly refractive,
and therefor does not show doubling.