Diamonds

It's not until the day he breaks that Heaven is able to hear him. It's also the day that Castiel learns, rather shockingly, that angels do, in fact, have tear ducts.

He doesn't know what to do, doesn't know why his eyes are leaking, or why his chest hurts so bad. All he knows is that the sound he is hearing – the sound that's somehow dragged it's way up from the pits of Hell and is now echoing through the stars– is horrible. It's the audible manifestation of someone in agony; Castiel didn't know all the pain and suffering of one man could be expressed through such a simple cry.

It was the sound of a soul being cut open and ripped in two!

The other angels, the ones who had gathered at the gates in preparation to descend into the pit, are quiet, but Castiel knows that they are experiencing the same phenomenon as he is. He can hear the tiny droplets as they hit the ground and shatter into millions of pieces. He can hear their wings rustling as they shift about uncomfortably, not understanding what is happening but knowing that it's the sound that's the cause of all this misery.

It reverberates all around them, filling their ears with it's mournful song. The angels are quiet, listening to the story of a hunter, a brother, and a father who was never truly there. Castiel silently weeps as the raw emotion of the tale sears every one of his nerves.

Minutes pass before the sound finally stops, and not even two seconds after it's abrupt end Castiel and his brothers are diving through the gate with a renewed determination in their eyes; anger running through their veins. They will do whatever it takes to get this man's soul back, even at the cost of their own lives because this man is special, he has a purpose.

Castiel knows he's special, because, after all, it's the first time in over a millennium where Heaven has willingly shed it's diamonds for the soul of a mortal.