Seems to me this should be divided into two questions. One…Is it
diamond? Two…if no diamond how important is the ID question?
To seperate diamond is not difficult. To zero in on which
non-diamond clear stone it may be is more work. Let me emphasise that
HOME GROWN results can be flawed, particularly via internet
interpretation. But here goes, use this at your own risk…
Loupe the stone. Pay particular attention to girdle and facet
junctions. See any chips, abrasions? If you see conchoidal
cleavages(looks like a clam shell) then it is no diamond. Diamond
fractures uneven, sometimes looks stepped.
Facet junctions… diamond polishes to a sharp line at junctions.
All other stones will be varying degrees of a rounded off look. Be
careful with this as what looks sharp at 5X may not be so at 15X. The
way to judge is to view from a perspective perpendicular to the facet
junction line. Have a light source opposite so it reflects on the
facets as you rotate the stone so each facet blinks at you, back and
forth. Catch it just as the blink changes. If you can see the
reflection ‘roll over’ the junction you can say if the junction is
rounded or not. That being said I did observe a confirmed diamond
once that appeared rounded.
Doubling…look thru the stone at opposite side facet junctions. The
line will appear crisp in a diamond. Doubly refractive stones wil
show varying amounts of fuzziness(doubling, because its doubly
refractive). View the stone from all angles because the amount of
doubling varies with optic axis. Grab yourself a known zircon to
illustrate this property if you’re not familair with it. Don’t assume
that if you don’t see doubling it is diamond.
You can pass the upside down stone over print to check the read thru
but I’ve found this not as reliable as has been reported.
These are indications only, not proof. Indications suggest specific
tests to come next. Be careful interpreting things. This is why we
have trained gemologists who get paid for the work, but since you
asked.
Ok, that’s part one. If you have determined it is likely not a
diamond you should think about how badly you want/need to know
exactly what gem species it is. Value wise, there’s not that much
difference between clear colorless stones, compared to diamond. From
here you need instruments and experience. I might ask myself if the
stone is pretty enough to set to warrant the investigation.
Or, (I might get stuff for this, even from me!) simply visit several
jewelers who buy from the public. You’ll get a pretty decent idea of
what you’ve got quick enough.