What is a Diamond?
Diamond is the name for the form of carbon that is produced when it is placed under extreme pressure and heat deep within the Earth. Diamond is one of the hardest substances known to man. When researching this part of this guide I found a great resource called Wikipedia which I will refer you to for some excellent further background reading about diamond:
Why an Engagement Ring?
The custom of giving an engagement ring as a symbol of a man’s commitment to his future wife supposedly originated from the Romans. The prospective husband gave his bride-to-be a ring which acted as a symbol of the cycle of life and eternity. This was performed at a formal ceremony.
Again, Wikipedia gives some great further reading on this if you are interested: