This gem was believed to possess the most marvelous virtues.
It gave victory to whomever carried it on his left arm,
whatever the number of his enemies. Panics, pestilences, enchantments
were all said to fly before it; hence, it was good for
sleepwalkers and for the insane. It deprived the lodestone of
its virtue, and one variety, the Arabian diamond, was said to attract
iron more powerfully than a magnet.
The diamond is the hardest substance known, a property referring
to its resistance to being scratched, rather than its resistance
to other forces, such as the strike of a hammer. Ancient
peoples believed that neither fire nor blows would overcome its
hardness, unless the diamond was macerated with fresh goats
blood. Cyprian, Austin, Isidore, and other church fathers,
adopting this notion, used it to illustrate the method by which
the blood of the Cross softens the heart of man.
If bound to a magnet, the diamond, according to the belief
of the ancients, would deprive it of its magnetic property.