So we had to go to Charleston, SC today......on the ride there I started rereading Order of the Phoenix. I've been kinda curious as to what the horcrux was that wasnt named by Dumbledore. From what I could gather, the last horcrux was either a relic of Gryffindor or Ravenclaw. Dumbledore made the statement that from what he can tell, all of Gryffindor's relics are safe. The natural deduction from that is that the last horcrux is a relic of Ravenclaw. I wish I had my copy of the 6th book on me, but if I remember correctly Dumbledore also mentioned he didnt know the whereabouts of any specific ravenclaw relics. So using what I've gathered from the series, I've tried to narrow down what might be the missing Ravenclaw relic, that is assuming Rowling even intended for there to be one, let alone have it act as a horcrux. Only one thing jumped out at me. The Mirror of Erised.
Reasons for thinking its a Ravenclaw Relic:
1. In the description of the Mirror in the Sorcerers' Stone it is described as having clawed feet.
2. "The Mirror of Erised is a mystical mirror discovered by Harry in a back corridor of Hogwarts School of Witchcraft and Wizardry in Harry Potter and the Philosopher's Stone. On it is inscribed, erised stra ehru oyt ube cafru oyt on wohsi - which, when reversed, reads I show not your face but your heart's desire. Also, "Erised", upon being reversed, is read as "Desire". According to Dumbledore, the Mirror "shows us nothing more or less than the deepest, most desperate desire of our hearts""-Wikipedia
I dunno, ir just sounds like a "clever, creative, and intelligent" item to have such a mirror anywho.
3. As a general rule, mentioning some odd item/event more than once without it effecting the plot in anywhere shape or form means that it will effect something later on in the storyline.......I might be overinferring here BUT...well, theres this:
"Rowena Ravenclaw was a witch admired for her incredible creativity. She is said to have conceived the ever-changing floorplan of Hogwarts. Ravenclaw House thus values in its members a sharp mind, wisdom, and cleverness. Rowena Ravenclaw is described by the Sorting Hat as having selected students according to intelligence."-Wikipedia
and twice in the series, once in the third book when Fred and George give Harry the Marauders Map, and a second time in the fifth book when Sirius is suggesting a place to hold the DA meetings, a certain place is mentioned:
A caved in passage on the other side of a mirror on the fourth floor. Both times as soon as the passage is brought into question the subject is quickly changed. I originally that that the mirror could be the Mirror of Erised when I first read it in PoA.....I didnt realize until this afternoon that the mirror on the fourth floor is referenced once again. Juat a random fact Rowling has found it neccessary to refer to twice? Quite possible Id say. I copied that bit from wikipedia on Rowena Ravenclaw for the reason that it stated she was responsible for the architecture of Hogwarts. Could she have incorporated a personal item of hers into the school? It's very possible I'd say.
4. The origin, whereabouts, and pre Sorcerers' Stone location are all unknown. As far as I can recall, Dumbledore seemed equally as perplexed as to the location of any of Ravenclaw's relics.
The Mirror as a Horcrux
1. It has the possibility of being a relic
2. Its well protected really. Who'd want to destroy a mirror that shows you your deepest desires as a physical part of you?
3. The opportunity to reach it was there. If my guess that the mirror on the fourth floor is the Mirror of Erised it was constantly accessible to Voldemort from the other side of the mirror. Not only that, It could have been the reason that Voldemort came to Hogwarts for the DADA teaching position in the first place. It could have been an excuse to "drop off" the horcrux or however it would occur. Thats assuming the mirror has been in Hogwarts the whole time. If not, its possible the Mirror has always been accessible to Voldemort.
4. If it is/was/always will be in Hogwarts, its entirely possible that Voldemort would gain some satsfaction out of making a horcrux out of an item thats right under Dumbledore's nose.
I dunno, its quite possible its all rubbish.....quite possible indeed.