Can opal be scratched by a nail?

Answer 1

It depends. Opals range between 5.5 and 6.5 on the Mohs hardness scale (how easy it is to scratch) which is kind of soft, so when used in jewelry they are usually coated with a polymer that provides a thin layer of protection against every day wear and tear.

Now, when you say "nail" do you mean finger nail (hardness 2.2-2.5, NO) or a metal nail you hammer? And if a metal nail, made of what metal? See, iron, nickel, and carbon steel are only around a hardness of 4-5 (won't scratch an opal), but some nails are made out of hardened steel which at 7.5-8 WILL scratch an uncoated opal.