For your reference, below are pictures of various fake nephrite jade eggs, mostly made of marble variants such as serpentine, onyx etc.
There are only 2 true jades: nephrite and jadeite. All other "jades" are fake jades or jade simulants
Instructors, trainers, and coaches of Kegel exercise must be very careful to offer yoni eggs to people who practice kegel exercise, because if the yoni eggs are fake or fraud jade eggs, it may cause troubles, ruin reputations, and even bring lawsuits.
Don't buy fake jade eggs made of marble stones, buy real jade eggs made of genuine nephrite jade.