are crystals harmful?

Bracelets are not crystals at all but just ornmental bands worn on the wrists or arms. The decorated jewels, stones & other materials on the bracelets may be considered as crystals. When things are radioactive, they are not crystals any more, they are hazardous materials & are fatal or harmful to humans. But some crystals emit very low frequency radiation such as quartz which is not harmful to our health, on the contrary they claim to bless their masters to have good fortune.

I just know some crystal are harmful to humans,like copper sulphste is harmful to your eyes and table salt is not hurmful