How To Tell Fake Onyx Gem I Purchased A Gem Online Via Emily's Gems,...for Just $3.00 And I'm Wondering How To Tell If Its Real Or Not

I Purchased a gem online via Emily's Gems,...for just $3.00 and I'm wondering how to tell if its Real or not - how to tell fake onyx gem

How can you tell if you have an Onyx, I bought true or false?

I realized that a rolling stone Onyx only $ 5 U.S. dollars, but the jewelry stores want $ 30 for