Dear Noel,
There are two types of common (no fire) opal from Peru that I’m aware
of, although I haven’t heard either referred to as Andean. One is the
blue that you’ve described and the other is a solid rose/pink. To my
knowledge neither is appreciably harder than any other opal which
means they’re not the most durable ring stones by far.
As for the $15 per carat price, that’s a lot more than I pay (a 7mm
round cab costs me $5) but prices often go up as you get farther away
from the source. Here in LA there are dealers at the big gem shows
that import it directly from India (where it’s cut) and the prices are
very low.
Beth