Is it Jet Onyx Obsidian French Jet or Plastic Tell the Difference Black Stones in Jewelry

THANK YOU FOR VIEWING MY OTHER GREAT VALUES. 6 1/4 Around Inside Including the Gap. Inside Measures 5 (2 3/16 Across Inside) Plus a gap of 1 1/4. High Quality Bracelet with Excellent Craftsmanship. extra fine vintage navajo sterling silver signed black onyx row bracelet.