Marcasite pendant or locket

A locket is an item of jewellery, usually a pendant worn on a chain around the neck, that is hinged and opens to reveal a space, sometimes called a "keepsake compartment", used for storing a a personal memento, such as a miniature, a photograph or strands of hair. Other styles of lockets are worn as a brooch or bracelet. They have been around in various forms since the 15th century, but reached the peak of their popularity in the 19th century, when sentimentality was part of the national psyche. They are most commonly made of gold or silver, often decorated with precious or semi-precious stones and come in many shapes including ovals, hearts and circles.