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Cutting Opals

Dear knowledgeable group-

I just got home from an interesting outing. I bought, though I did
not need, a man’s rock collection. I do not know what most of the
rocks even are. The man was unable to remember most of them due to
chemo treatments and a major illness. In a little zip lock bag are 15
opals. These are rough rocks but unmistakably opals. My question is
this- What do I do with them? Is there somewhere to have them made
into cabs suitable for jewelry? Some of them are actually very fiery
and beautiful. They are mostly whitish and grayish with pastel fire.
If there is anyone on the list that can steer me towards information
I would appreciate it.

I also have no idea how to figure out what some of the other ones
are. I have a great big crystal looking rock that is about 30" long,
and about 4" square. It looks layered and it is semi transparent. The
man thought it was mica- but I do not think it looks anything like
mica. It is a yellowish gold color something like a citrine crystal.

Help if you can, please.

Jean Menden


Opals are easy! Most lapidaries are more than capable of finishing
tough into cabs for jewelry. I have done a few hundred myself.
Without actually seeing the rough, it is impossible to say whether
your rough is even worth finishing, or what you might get out of it.
Opals are by no means a “sure thing” and disappointments are common
after grinding off the outer crust. Size is also important in
determining whether it would be worthwhile to proceed. You could even
finish them yourself without the need for machinery or special
equipment. All you need is a bit of patience and some simple

Dick Davies

are. I have a great big crystal looking rock that is about 30"
long, and about 4" square. It looks layered and it is semi

My guess would be the selenite form of gypsum.

Al Balmer
Sun City, AZ

What is this? Great minds having the same thought?? I “inherited” a
bag of opals similar to what you describe!

I have other bags and coffee cans, but nothing as spectacular as you
describe. Perhaps whomever responds with some real info will help us
both. Two birds with one email!

Hi Jean,

Opals are very easy to cut, they are so soft. You can rough it out
using a mizzy wheel, and use sandpaper to refine and cerium to
polish. You must use care and keep it wet, to reduce heat. Also use
care in not removing the color. Its very easy to grind away all the
beauty As far as identifying your other treasures, pictures help a


Hi Jean…

I cut stone, in fact, I started with opals…if you want me to look
at anything, just send me pictures. How big are the opals? are they
chips or chunks that can be sawed up? Were they stored in water or
glycerine or dry?


Concerning the big crystal: There are micas of many different colors.
It can be semi transparent and it would definitely be “layered” if it
is a mica. It is said to occur in “books”, it has such a distinctive
cleavage. Some kinds used to be used for windows and lamps and stove
windows years ago. Get a book (no pun intended) on minerals and key
it out. Especially consider the hardness. Mica is quite soft compared
to a lot of minerals. Phlogopite is a gold toned mica often found
associated with gold deposits. If a mica crystal was thirty inches
long it most certainally would be a collectors item and you wouldn’t
want to try to make jewelry stones out of it. I only know of one mica
(lepidolite) that is sometimes used for decorative stones. But I have
never heard of a mica crystal being that big!!Square? Is it square in
cross section? I think mica is hexagonal. Square?

Rose Alene

Here in Portland, OR I list my name with the local lapidary shops or
rock shops and let them know that I do cutting and polishing of
material. If you have a rock shop close to you contact it to see if
they can recommend one to cut you opals.

You might also be able to find a rock club in your area who could
give you a reference for a cutter.

Larry E. Whittington
Larry E. Whittington Lapidary

It’s very hard to advise about opal cutting. It’s been pointed out
that precious opal is among the easiest of gems to fashion and polish
because of its relative softness and adaptability to lapidary
techniques. True, but that’s not the whole story.

Judging rough to determine whether it’s even worth cutting, or
determining how the best stones can be made from it are matters,
where experience and judgment come in. It all depends on the type
and source of precious opal – there are many – and how the color
lies; whether the play of color is directional, whether it’s
"skin-to-skin" or thin color bars that can be oriented and cut, among
many other things. Possibly there are sand, “cotton” and other
inclusions and subsurface cracks to consider.

I recommend you locate someone with experience in these matters to
advise you, possibly through a local gem and mineral club. Precious
opal can be valuable and is a rapidly diminishing resource. Take
your time.

Rick Martin

The first step to do is to sand/grind the side of the rough piece of
opal. This will show where the best layer of colorfull gem is. From
there you can cut the base and the dome to get the bst look.