Not hard as a Diamond.
*** Hello, We would be happy to replace your center stone under your Lifetime Stone Guarantee! Feel free to email, chat or call a Customer Care Advisor so they can send you the proper forms. Please note that our Nexus Diamond lab created alternative is not as hard as a diamond and on the Moh's Hardness Scale it will be graded as a 9.1-9.2 while a mined or lab grown diamond is graded at a 10. -Customer Care Advisor ***