Complex sentence: The finest quality natural pearls have been highly valued as gemstones and objects of beauty for many centuries, and because of this, the word pearl has become a metaphor for something very rare, fine, admirable, and valuable.
Split into simpler sentences: The finest quality natural pearls have been highly valued as gemstones and objects of beauty for many centuries. Because of this, the word pearl has become a metaphor for something very rare, fine, admirable, and valuable.