Understanding Opal Cracking: Causes & Prevention

Question
why opals crack?what we do to avoid cracking?
g          
         thank you

Answer
The hardness of opal is rated at 5.5 - 6 on the Mohs Scale, with 10 being the highest value. To give you some perspective, minerals like talc have a rating of "1" and diamonds, "10". Talc is so soft that you can scratch it with your fingernail and was previously used as a component for baby powder, while diamonds were once considered the hardest material on earth. In between lie gems like opals which are as hard as glass, which is why opal jewelry is not advisable for daily wear nor should these gems be put in an ultrasonic cleaner. To clean your jewelry, just use warm soap and water.