siriuswriter
Senior Member
All known methods of Horcrux destruction are as deadly as the murder needed for its creation. For example, the earliest known method is administering basilisk venom to the Horcrux, the only cure for which is phoenix tears, an extremely rare substance. Other known methods are Fiendfyre (as evidenced by its destruction of Rowena Ravenclaw's Diadem), which requires extreme skill to control and the Killing Curse which seems to be capable of destroying a Horcrux if it is animate, given that part of Voldemort's soul contained in Harry Potter was destroyed when he was struck with the Killing Curse in 1998.[5] However, Harry Potter was never an intentional Horcrux and so it may not work on a proper, animate Horcrux (like Nagini), probably having unforeseen side effects.
Harry Potter was not destroyed as a Horcrux in the Chamber of Secrets because Fawkes' tears saved him and hence the "receptacle" (Harry) was not then destroyed beyond repair.[2]
Albus Dumbledore,[4] Ron Weasley, and Neville Longbottom[5] used Godric Gryffindor's Sword to destroy Marvolo Gaunt's Ring, Salazar Slytherin's Locket, and Nagini respectively. This was only achievable as the sword is a Goblin-made artefact, which can absorb qualities that strengthen it. When Harry Potter slew the Basilisk in the Chamber of Secrets,[6] the sword was imbued with Basilisk venom and became capable of destroying Horcruxes, as Basilisk venom by itself is destructive enough a substance to destroy a Horcrux.
Harry Potter and Hermione Granger used Basilisk fangs from the Chamber of Secrets to destroy Tom Riddle's Diary and Helga Hufflepuff's Cup, respectively.[5]
[http://harrypotter.wikia.com/wiki/Horcrux]
[bolds mine]
So, the only reason that the Sword could destroy a Horcrux was because it was dipped in Basilisk venom. Oh, and Fiendfyre DID destroy the diadem Horcrux.
It helps to get the actual facts.