I don’t know of any easy way to tell a micro-diamond 1/2 mm wide or
less from other glassy material.
I wouldn’t be so interested except these samples are from a fast
moving mountain river which “tumbles” loose stones over miles of
outcroppings and they seem to carry C as volcanic soot. The jet
black powder I have found in some poly-metallic veins is soot in a
"bubbly" host rock and I assume it is C soot.
I googled on the Wawa Ontario diamond find. That is from the last
decade and the host rock is not kimberlite. The area was thoroughly
prospected since the 1800s when some gold mines were started there.
So diamonds are the prospecting needle in the haystack.
If I cannot find a quick and easy assay method here, I may send them
to the DeBeers lab at U of A. Probably nothing but why not find out
for sure? They are of course studying the micro-diamonds from the
kimberlites in Northern Alberta.