Rough Opal

What is rough opal?

Rough opal is the natural gemstone exactly as it comes out of the earth. It has not been cut, shaped, or polished by a gem cutter. In this raw state, it often looks like a piece of ordinary rock or clay with flashes of bright color hiding inside. Miners extract these raw pieces directly from the ground and sell them to professionals or hobbyists who want to cut the stones themselves to reveal the true beauty inside.

How can you tell if rough opal is valuable?

The value of the raw stone depends entirely on the bright colors visible inside the opal. A valuable piece will show vivid flashes of red, blue, or green even before it is completely polished. The stone must also be solid and free from deep cracks or heavy sand inclusions. Professional lapidaries often shine a bright light through the raw pieces to see how deep the color goes and to check for hidden flaws that might affect the final gem quality before they start cutting.

How do you know if rough opal will have color?

Finding color in raw material can sometimes be a guessing game. Miners and cutters usually rub a small section of the raw stone on a grinding wheel to expose what is hiding under the surface. This process is called facing the stone. Wetting the raw material with water is another very common trick. The liquid temporarily acts like a smooth polish and makes the hidden play of color much easier to see with the naked eye.

How much is rough opal worth?

Pricing raw opal is very different from pricing finished gems. Rough opal is usually sold by the gram or per piece rather than by the carat. Low grade material with very little color might sell for just a few dollars per gram or per piece. However, a parcel of raw opal showing bright red fire and a clean base can be worth thousands of dollars. Buyers carefully evaluate the potential yield, which is how many finished gems they think they can successfully cut from the raw material.

Can you cut and polish rough opal yourself?

Yes, cutting and polishing raw opals is a very popular hobby worldwide. You do not need to be a professional to learn, but you do need the right lapidary equipment. The process requires diamond coated grinding wheels and water to keep the stone cool. Because the material can be relatively soft, it is a great stone for beginners to practice shaping. Many hobbyists enjoy creating their own jewelry starting right from the raw earth. Learn more about opal polishing in our guide to opal polishing.

What is potch in rough opal?

Potch is a natural form of common opal that does not have any colorful flashes. It is made of the exact same silica material as precious opal, but the internal silica spheres are not stacked in the right orderly pattern to create color. Potch can be gray, black, or white. In raw stones, it often acts as a natural backing. For example, the dark potch found in raw black opals is exactly what gives the finished gemstone its highly valuable dark background. In boulder opals, the host rock is ironstone, as opposed to potch.

Is buying rough opal risky?

Buying raw stones always involves some level of risk. Because you are looking at an uncut rock, it is impossible to know exactly what is hiding inside until you start cutting. A beautiful flash of color on the outside might only be a very thin layer, or the stone might contain hidden cracks and sand spots deep inside. To reduce this risk, many beginners prefer to buy rubbed stones, which are pieces that have been slightly ground down so you can clearly see the color bar before you commit to cutting a solid opal.