The Hufflepuff hourglass in the Hogwarts Entrance Hall for recording House Points is filled with yellow diamonds (JKR:Tw, Pm).
J.K. Rowling told a fan on Twitter that the Hufflepuff hourglass is filled with diamonds because members of that house are "diamonds in the rough" - a phrase meaning "full of potential."
Many mentions or comparisons to diamonds:
- Fred and George gave their mother Molly "a brand-new midnight blue witch's hat glittering with what looked like tiny starlike diamonds" for Christmas in 1996 (HBP16).
- A sign on the Firebolt in Quality Quidditch Supplies said the ash handle was "treated with diamond-hard polish (PA4).
- Fleur Delacour describes the Christmas ice sculptures at Beauxbatons as "huge statues of diamond, glittering around ze place" (GF23).
- When Wormtail heated the cauldron for Voldemort's rebirth, the surface of the liquid "was alight with sparks" as though "encrusted with diamonds" (GF32).
- The giant crystal bell-jar in the Time Room at the Department of Mysteries gave off a "dancing, diamond-bright light" (OP34)
Old French diamant, from Medieval Latin diamantem
When JKR was eleven, she wrote a series of stories about people who owned seven cursed diamonds (JKR:FAQ).