first a notch is retouched into one side
then the end is
removed
the process can be repeated at the other end
the medial part
can then be made into a (for example) scalene triangle microlith leaving
a micro-burin 
the micro-burin is so called because of it's similarity to a real burin
and was regarded as a tool - it is now recognised as a waste product of
microlith manufacture and though it retains the name it has nothing to do
with burins
