Distinguishing genuine black onyx from fake or dyed versions can be challenging, but here are some methods to help determine its authenticity: 　　Color and texture: Real black onyx should have a smooth, uniform black color with no unusual patterns or variations. It should feel cool and smooth to the touch. 　　Streak test: Rub a piece of unglazed porcelain tile across the black onyx. If the streak left behind is white, it’s likely real onyx. A black streak indicates a fake. 　　Transparency: Hold the onyx up to a light source. Genuine onyx is generally translucent, allowing some light to pass through. 　　Weight: Real onyx is denser and heavier compared to plastic or glass imitations. 　　Scratch test: Onyx is quite hard, so it should not easily scratch with common household items. 　　Consult a professional: When in doubt, consult a gemologist or a jeweler for a more accurate assessment using specialized tools. 　　These methods can provide a reasonable indication of whether black onyx is real or not, but professional expertise is often needed for a definitive assessment.