This is a gorgeous 100 carat diamond engagement ring. A carat is a unit of measurement used in the diamond industry to determine the weight of a diamond. One carat is equal to 200 milligrams. An engagement ring is a ring indicating that the person wearing it is engaged, i.e. he has made a commitment to marry or marry. The ring is presented as an engagement gift from a partner to his future wife when he proposes marriage or directly after accepting a marriage proposal. An engagement ring represents a formal agreement of future marriage. Engagement rings are mostly worn by women. The rings usually contain precious stones and most often diamonds. Around 150 million carats of diamonds are been produced from mines worldwide each year. The most expensive engagement ring ever in history is the ring given to Kelly by Prince Rainier III of Monaco. It was worth $4 million and its prize rises constantly as today it is worth $38.8 million.