5. Pearls dissolve in vinegar
You can find a grain of truth in this statement. Of course it would take quite some time plus you would need to crush them first. It is very unlikely that you are going to carry out such an unusual experiment to test and prove the fact.
6. Opals attract bad luck
In Ancient Rome people considered opals to bring good luck. Times have changed and nowadays this precious stone is thought to attract bad luck. It is up to you to decide whether you believe this prejudice or not. The fact is that black opals are very unique and rarely found hence they are expensive.