Opal

An opal is a mineraloid composed mostly of silica and water. Opals can express every colour in the visible spectrum, although the most common colours are white and/or green.

While tidying up the cabinets next to the mantelpiece at 12 Grimmauld Place in 1995, Harry Potter came across a large blood-filled crystal bottle with a large opal set into the stopper. There was a cursed opal necklace for sale at Borgin and Burkes that Draco Malfoy purchased and gave to and Imperiused Katie Bell in an attempt to assassinate Albus Dumbledore.

Appearances

 * Harry Potter and the Order of the Phoenix
 * Harry Potter and the Half-Blood Prince
 * Harry Potter and the Half-Blood Prince (film)
 * Harry Potter and the Half-Blood Prince (video game)