Irish Friendship Rings have been a tradition for 300 years, and often have a green gem in the shape of the heart with them. The wearers are demonstrating significance and loyalty towards their friend.
The typical Irish friendship ring consists of the band forming two hands which are holding a crowned heart. You can find many pictures of this type ring with a simple search on a popular engine.
Irish friendship rings are typically made of pewter or other silver metals. The feature Celtic symbols such as heart or hands that are knotted together. Legend says that those who wear the rings will remain friends for life.