The symbol of Rings:

Engagement and wedding rings are worn on the left hand on the third finger from the thumb, because of the ancient belief that a vein ran directly from that finger to the heart. 

The shape of the ring indicates the boundless and seamless flow of love.  Many brides like to choose their birthstone for their engagement ring and surround it with diamond.

Birthstones:

January - Garnet

February - Amethyst

March - Aquamarine

April - Diamond

May - Emerald

June - Pearl

July - Onyx

August - Peridot

September - Sapphire

October - Opal

November - Topaz

December - Ruby