Practical opal testing

Hi all

i was just checking the archives for some info on Opal tests, and
there were afew threads on the testing, one was by Don Rogers 2002,
i tried to google him but it seems it was sort of a dead end, i was
wondering if in simple terms there was a test for being able to tell
if what you are purchasing is a yellow opal or chalcedony, i know
hardness test is the way to go, i am just wondering ona practical
sense what would be a hardness test, scratching the stone with a
hard material like tool steel ? or? i know chalcedony does not want
to scratch that way, I had purchased a few peices of really nice
looking yellow golden opal, but I just don’t know for sure since the
price was low and the source was reputable, but had a nagging
question on the price. any one out there with a practical test for
me to perform at the bench? ??

thanks Hratch

if what you are purchasing is a yellow opal or chalcedony 

I suppose I could give you long winded gemological answer, but how
about just using your eyes. If chalcedony looks like opal, it is o.k.
to pay for it opal price, and vise versa.

Leonid Surpin