The House of Tibara, Opal Specialists - Frequently Asked Questions About Opals

Here is a list of the most frequently asked questions we have answered over the past 25 years. If you have a question that isn't answered on this page, why don't you drop us some email.

What factors determine value?
Click here to learn more.

What are opal's physical characteristics?
Soft. On the Mohs' scale of hardness opal measures just above glass: glass = 4-4.5, opal = 4.5-6.

How do I know the opal will not crack or craze?
Experience and trusting the seller!

Can I cut opal without machinery?
Yes, with sandpaper (wet&dry) going from 240 to 1200 grit, then polish using optical polish on leather.

What kind of machinery cuts opal best?
Diamond - which cuts with low heat. It also is available in finer grits that won't chip the opal.

Is opal an investment stone?
Yes, in gem quality. Also unique stones (fire patterns and unique colorations).

Rough vs. Cut Opal?
If you buy rough opal and cut it yourself, you should be able to appraise the cut stone at 5 times what you paid in rough conditon.

How do you judge the yield on a rough stone?
A rough stone should yield 20% or better of its volume once it's cut. ie. a rough 5 gram stone should yield a 5 carat cut and polished opal. A rough stone which yields only 5% of it's volume is a poor yield.

What causes the play of color in opals (the fire?)
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Why is opal kept in water?
For display only, since the refractive index of water and opal are very close. Opal in water will simulate what opal will look like when it's polished. Otherwise, keep it dry.

Do you buy opal in Australia?
We buy our opal from the miners -- in the comfort of our living room -- negotiations favor us that way. That helps to keep our costs down. Imagine what our opal prices would be if we had to apply the cost of the trip to Australia or Brazil to each ounce of opal that we buy! You don't have to imagine it very long... just look at the prices of our competition and you'll see what we are talking about.

How do you store opal?
Store opal safely, well padded. Remember that the hardness is about the same as glass. Rough opal can be stored wet or dry on a shelf, drawer, etc. Cut and polished opal should be stored where it will not be subject to banging or scratching by harder materials like gold, diamonds, garnets, etc.

Is it OK to put opal in a safety deposit box?
Only if you place the opal in water, or in a container that is hydrated. Safes that hold safety deposit boxes have their air dehydrated to one half of one percent, and the opal may lose water through the dehydration process.

Can I soak opal in...
... glycerine? No, glycerine is hydrophilic and can draw water from the stone.
... oil? No, can discolor as stone, and is very hard to clean off.
... water? Yes.
... wet towel? Yes.

Why does the fire disappear on rough opal until you put it in water?
Water has about the same refractive index as polished opal, so rough opal in water is a preview of the cut and polished opal.

How do I know the opal I buy will be stable?
The reliability of the source... the person that you buy from.

What does stable mean?
Stable means that the opal, under normal heat and climactic conditions, won't crack or craze.

What is our return policy?
We will replace a parcel that goes bad within 30 days after purchase, but before cutting or grinding ... once you cut or grind it you must assume total responsibility for it.

How can you buy from us through the mail?
Well, you can click here to email us. We'll be happy to correspond with you. Let us know what you'd like to buy, and we'll contact you by phone for credit card information.

What is opal?
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Where is opal found?
Australia, Brazil, Java Indonesia, Virgin Valley-NV, Gabbs-NV (blue), Boise-ID, Oregon (blue), Mojave, Canada, Ethiopia, Austria, Honduras, Mexico.

What different kinds of opal are there?
Precious.
Potch/common (desirable if translucent red, yellow).
conc: Replacement of organic material, can be partial.
cachalon: A chalky base that sticks to your tongue.
Faceting: Translucent material with fire that can be faceted like diamonds.

How is opal formed?
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Where is opal found?
Alluvial stream bed or alluvial field deposit, through the erosion processes, and in various strata.
gas pockets (ID).
thunder eggs (OR).
fossil (opalized) shells and dinosaurs (NV, Australia).
wood replacement or other plant replacement (NV, Australia).
Opal that fills cracks in hard rocks (boulder opal) (ID, Australia).
Man made opal.
Rhiolite matrix.
Sandstone matrix (Honduras).

Why does opal crack or craze?
It can crack or craze naturally, if the water content of the opal is too high. Or if it's banged around improperly, set in jewelry improperly, or during cutting & polishing if it gets too hot.

How to store opal?
Mineral or other oils: no
Glycerine: no, glycerine is hydrophilic and can draw water from the stone.
Safety deposit box: no, the air is dehydrated to 1/2 of 1%. It's possible that the opal could lose water. Store in water or in a sealed plastic bag with a wet paper towel & pad well.

What is cracking and crazing?
Crazing is like when a rock hits an automobile window... the glass shatters but is held together. Crack means that the piece comes apart or has the potential to come apart.

What are opal's characteristics compared to diamonds?
Diamond hard/brittle ... 10 on the Mohs' scale.
Opal soft/brittle ... 4.5 to 6 on the Mohs' scale.

Can I keep opal in a jewelry box?
Yes, but don't throw it in with harder stones & metal. Treat as a very fine gem. Place pendants or pendant holders and rings in a ring rack.

Opal myths:
Opal is NOT bad luck if it's not your birthstone! The myth was perpetuated by diamond dealers in the late 19th century because opal was diamond's biggest competitor.

Why buy from people who deal direct from mines?
Generally, opal is more expensive when bought at the source. We have people we buy from who know the field, the mine depth, and how it's mined. There is also a historical perspective on some fields as far as stability is concerned. For instance, opal from the Mehi field or 19 mile is considered unstable. Also, opal found more than 50 ft deep is not considered as stable, due to the release of pressure. Pressure keeps the water in the opal until it's brought up from the mine. Then it can crack or craze as the pressure releases. That's why we buy from long term associates who know or try to find out where the opal is mined.

What about finished stones? What should I know?
Know that some finished stones are made in sweat shops, and are not generally cut with water. These shops use silicone carbide instead of diamond, resulting in a stressed stone that may craze. Know where the stone was cut!

Why use epoxy instead of dopping wax?
A miner from the Lightning Ridge opal field in Australia sent 5 parcels or rough opal to 5 different cutters. Those that used dopping wax had the highest cracking rate. Those that used epoxy had the lowest cracking rate.

Why buy in the United States?
First, there's less waiting time. We send a couple of parcels to our clients and they can choose their lots. Buying in Australia takes a long time, and many customers that buy from Australian sources who are unhappy do not return bad batches since it's too much trouble... even though there are many ethical Aussies who care if you find a problem and will take care of you.

What are fabricated opals?
Triplets: Opal is sandwiched and glued between a backing and a quartz cap.
Doublets: A thin piece of opal is glued to a backing or potch, jade, glass, etc.
Overlay: A doublet with a bolder opal backing.
Mosaics: Many small pieces of opal glued on a black surface together using small pieces.
Intarsia: Opal is combined with various materials, lapis, malachite, sugilite, jades in geometric patterns or other designs (like inlaid wood).

Haill, Robert G. Opals of the Never Never, Castle Books, 1982.

Barnes, L.C. and Townsend, I.J. Opal, South Australia's Gemstone D.J. Woolman, Government Printer, South Australia, 1982.