There are a few ways for you to tell if the Peruvian blue opals you’re looking at are not real. The most obvious clue is that fakes will be relatively cheap – around $30-$40 for an entire strand of beads. Since the real ones are growing more and more rare, you would never be able to buy a string of beads for so cheap. After all, jewelry made with the real thing will be several hundred or even thousands of dollars.
Generally, if a company is making fakes, they will take white opals and then work to dye them. If you’re worried that you might be buying fake blue opals, you should take a good look at the stones. In a lot of cases, you can tell that it is just a dyed white opal by looking with the naked eye. The blue coloring will be uneven, especially when you turn the stone so the light hits it from different directions. This is very useful if you’re thinking about buying an opal inlay ring with blue opal, since you won’t be able to tell by the price in some cases, and the weight will be difficult to determine due to the rest of the ring.