The sun sign of Aries is ruled by the planet Mars, and with Mars being the roman god of war, you'll find the diamond bears a fascinating parallel to this mythological theme. Diamonds are said to grant courage, physical strength and power to the wearer and on reading through ancient antiquities, you will find that ancient roman and Indian soldiers wore diamond rings to bolster their conquering spirits and bring on victory in battle.
On a more modern simile, diamonds have been used to tame hostilities in the battle of the sexes. From ancient times until now, the gifts of a sparkling diamond has been known to quell the jealousy or anger of a lover in the most delightful--and speedy-- way. No wonder they say diamonds are a girls best friend!! Another pleasant property of the diamond it is said, is its ability to enhance sexual responsiveness and fertility. I wonder why!
So, bravery, physical strength sex drive and fertile are qualities attributed to Aries, who are also known for their pioneering drive to forge new trails and rise to every challenge. Think about it, with Mars endowing them with healthy sexual vigour channelled into their powerful and energetic approach to life, no wonder the diamond associated with the element of fire, brings out the Arian personality with such egotistical overtones.