Chris, First of all a word of caution. There is much misinformation
about fire opals from Mexico. The term “Fire opal” was originally a
label given to jelly opals with a red or orange body color. The
color resembled the color of a wood camp fire. Most of this opal has
no “fire”, as is thought of in brilliant colors associated with
precious opal. Gem grade Mexican opals have body colors from clear
white, to red, to orange, to yellow and mixtures of all the above.
All “Gem grade” opals have the brilliant play of opal flashes. Clear
white stones with very intense color must be carefully mounted to
show the color. Very little of the “gem Grade” red and orange
Mexican opals ever reaches the US. Word is that the large gem
cutting corporations have buyers stationed near the mine sites to buy
all the top grade stones. Many rough stone dealers who have tried
to buy gem grade opals at the mine sites were unsuccessful. Mexican
opal is also very unstable. Stones can craze in a matter of days.
There are many theories about why this happens. None of the reasons
really matter that much to me. What I would like to know is how to
tell which ones will craze and which ones are stable before I cut
them. I have heard that a large find of similar volcanic opal has
been discovered in Brazil. Maybe someone else has news for you.
Phoenix, Arizona, USA