A diamond is a very valuable gemstone with remarkable physical characteristics: it has the highest hardness and thermal conductivity of any bulk material and a relatively high optical dispersion which results in its characteristic luster.
For Christmas, in 1996, Fred and George Weasley offered their mother a brand-new midnight blue witch's hat glittering with what looked like tiny starlike diamonds. Diamonds were among the gems set into Muriel's tiara, as well as moonstones.
- Harry Potter and the Prisoner of Azkaban (Mentioned only)
- Harry Potter and the Goblet of Fire (Mentioned only)
- Harry Potter and the Order of the Phoenix (Mentioned only)
- Harry Potter and the Half-Blood Prince
- Harry Potter and the Deathly Hallows