Advice please

Hi --

First of all, I found the lemon test (from this site) to be an
invaluable tool in selecting stone for the kitchen and I am so thankful
I happened upon it.  Lately I have seen some onyx counters featured in
model homes.  I am guessing that some onyx may not really be onyx, just
as "granite" maybe not be granite, but can you compare the two stones
for durability, hardness, and practicality??  How would using so-called
onyx on a bathoom counter compare to using so-called granite??

Thanks,
Linda Warren