Unless there is a reliable, objective test for identifying the
stability of an opal, the statements that stable opals aren’t fragile
or stable opals don’t craze are simply circular arguments, since the
only way to identify a stable opal is by the fact that it has not
(yet) crazed What a great statement. It really sum’s up the arguments
on opal. There is no test other than time that I am aware of.
I have been an Opal dealer for the last ten years or so. I have
heard statements from contemporaries to the effect that there are
two types of opal, those that have crazed, and those that will craze.
I know that this is a pessimist view of opal, but depending on the
source of the opal, there might be some truth to it.
As you state, there is no test other than time to know for sure. I
will share my observations though.
The opals from the US are not very stable. Of course there are
exceptions, but the Nevada Opal will sometimes craze over in a mater
of minutes. The Idaho opal is also known to be unstable, but when cut
for triplets, it has a good life expectancy. The Oregon Opal is
another that may or may not be stable. I have no knowledge of the
opal from Louisiana, but that is not a major source.
Mexican opals range across the board from very unstable to rock
solid. Those in matrix seem to be more unstable. I would only
purchase rough or cut stones that have been dry for a few years. The
finest opal I ever sold was a Mexican opal faceted into a 7.5 ct
trillion. It had a water clear body with incredible fire. This stone
was about three or four years past cutting and I had it under lights
for over a year before I sold it. It was rock solid. I miss it.
Brazilian opal can also be some of the most stable of opals. Some
are very hard, and very clear. They are also very hard to find now.
My friends in Australia have a saying that Andamooka is for ever.
The Andamooka crystal is great. It has a repetition of Never Crazing.
I have seen stones that were 50 years old that looked new.
Lightening Ridge opals are said to be Craze free. There are some
fields there that have produced opals that are prone to crazing. It
depends on the depth of the opal seams. The deeper, the more prone to
crazing. Some research is needed to find out which field the stone
came from to determine it’s potential.
Coober Pedy. Some of the fields will produce very sound opal. Some
will not. The one’s that will that I know of are good are the Dead
Horse Gully and the Olympic fields. My suggestion here is that if the
opal has a grey base color, beware of it. The white base and crystal
seem to be much more stable I will yield my opinions on this to some
of my Australian friends who have more experience in that area than I
Other Australian fields are mixed. The Queensland fields of
boulder opal and Matrix opal are great. The Mintabie fields have
produced some great stones but again, look out for the grey based.
Some are prone to crazing while others are rock solid. The White
based from here is top. The Lambina fields is now producing some
great opal. It tends to be hard, and some is prone to chipping, but I
have not seen any crazing as yet. When I say hard, this opal and
some of the Brazilian opal is running around 7 in hardness. Great for
faceted stones, but somewhat brittle.
There is opal from Ethiopia, Honduras, and points in Africa that
are now producing opal. Some are good, some aren’t. I have little
experience with these locations so I will offer no opinions as to
The bottom line is that you need to know where your opal is coming
from, and you need to do the research to verify the potential for a
long life stone from that area. There is always the exceptions to
what I have stated above, but you should know that you may be taking
a risk. Just remember though, that the greater the risk, the greater
My personal rules for Opal are this;
For rough opal, if it has been dry for two years, and no crazing,
it should be OK. As I have no idea how you worked the stone, if you
cut it, it is yours with out any guarantee. If it is uncut, IE the
same as I sold to you, and there is a problem, we will work it out to
where we are Both happy.
If it had been cut and under lights for three years, I will
guarantee it if it has not been set. I do not offer opals for sale
that have not met the three years criteria.
Opals can be most rewarding. They are the reason I am in the Gem
business. They can also be disappointing. I have a bag of what I call
my heart breaks. They are the ones that didn’t meet my criteria for
sales. IE, they crazed while setting in my show cases. They are
greatly outnumbered by my good stones, but they do exist. I also have
several hundred that in my view are rock solid stones and they make
the Opal business most enjoyable.