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Once again, I find myself with two persons who don't have anything in common and are, right now, arguing.

"That is not the real diamond I lent you! You thief! Where is it?" the lady shouted, pointing to the small stone on the hand of the man.

"This is the real diamond!" the man objected. "In fact, I have proof!" he added, taking a hammer out of his briefcase. Why he had a hammer in the first place, I didn't want to find out.

Placing the stone on a table, he carefully aimed the hammer at the gem and with one big arc, hit the stone with so much force that the table quivered. The gem remained intact.

"See? It didn't break. Therefore, it is a diamond, which is the hardest mineral on Earth!" he cried triumphantly.

"You have a point," said the woman reluctantly, with a voice sounding of defeat.

Is that her real diamond?

real diamon broken up due to hammering.
Diamond is hardest material on earth due to its hardness it becomes brittle.