The sword Anglachel was forged anew for him by cunning smiths of Nargothrond, and though ever black its edges shone with pale fire; and he named it Gurthang, Iron of Death.

(Silm, Chapter 21, Of Túrin Turambar)

At that many of the Orcs looked back in dismay, and then out came Túrin leaping, waving as if to men behind, and the edges of Gurthang flickered like flame in his hand. Too well was that blade know to the Orcs, and even before he sprang among them many scattered and fled.

(UT, Narn i Hín Húrin)

Then Túrin sprang about, and strode against him, and the edges of Gurthang shone as with flame; but Glaurung withheld his blast, and opened wide his serpent-eyes and gazed upon Túrin. Without fear Túrin looked into them as he raised up the sword; and straightway he fell under the binding spell of the lidless eyes of the dragon, and was halted moveless.

(Silm, Chapter 21, Of Túrin Turambar)

But here is a thorn sharper and longer than the knife of Azaghâl."
And Turambar swept Gurthang from its sheath and stabbed with it up above his head, and it seemed to those that looked on that a flame leapt from Turambar's hand many feet into the air. Then they gave a great cry: "The Black Thorn of Brethil!"
"The Black Thorn of Brethil," said Turambar: "well may he fear it. For know this: it is the doom of this Dragon (and all his brood, it is said) that how great so ever be his armour of horn, harder than iron, below he must go with the belly of a snake.

(Silm, Chapter 21, Of Túrin Turambar)

Then Turambar summoned all his will and courage and climbed the cliff alone, and came beneath the dragon. Then he drew Gurthang, and with all the might of his arm, and of his hate, he thrust it into the soft belly of the Worm, even up to the hilts. But when Glaurung felt his death-pang, he screamed, and in his dreadful throe he heaved up his bulk and hurled himself across the chasm, and there lay lashing and coiling in his agony. And he set all in a blaze about him, and beat all to ruin, until at last his fires died, and he lay still.
Now Gurthang had been wrested from Turambar's hand in the throe of Glaurung, and it clave to the belly of the dragon.Turambar therefore crossed the water once more, desiring to recover his sword and to look upon his foe; and he found him stretched at his length, and rolled upon one side, and the hilts of Gurthang stood in his belly. Then Turambar seized the hilts and set his foot upon the belly, and cried in mockery of the dragon and his words at Nargothrond: 'Hail, Worm of Morgoth! Well met again! Die now and the darkness have thee! Thus is Túrin son of Húrin avenged.'

(Silm, Chapter 21, Of Túrin Turambar)

There now Glaurung lay, with jaws agape; but all his fires were burned out, and his evil eyes were closed. He was stretched out in his length, and had rolled upon one side, and the hilts of Gurthang stood in his belly. Then the heart of Turambar rose high within him, and though the Dragon still breathed he would recover his sword, which if he prized it before was now worth to him all the treasure of Nargothrond. True proved the words spoken at its forging that nothing, great or small, should live that once it had bitten.
Therefore going up to his foe he set foot upon his belly, and seizing the hilts of Gurthang he put forth his strength to withdraw it. And he cried in mockery of Glaurung's words at Nargothrond: "Hail, Worm of Morgoth! Well met again! Die now and the darkness have thee! Thus is Túrin son of Húrin avenged." Then he wrenched out the sword,..

(UT, Narn i Hín Húrin)

Then he drew forth his sword, and said: "Hail Gurthang, iron of death, thou alone now remainest! But what lord or loyalty dost thou know, save the hand that wieldeth thee? From no blood wilt thou shrink! Wilt thou take Túrin Turambar? Wilt thou slay me swiftly?"
And from the blade rang a cold voice in answer: "Yea, I will drink thy blood, that I may forget the blood of Beleg my master, and the blood of Brandir slain unjustly. I will slay thee swiftly."
Then Túrin set the hilts upon the ground, and cast himself upon the point of Gurthang, and the black blade took his life.
But Mablung came and looked on the hideous shape of Glaurung lying dead, and he looked upon Túrin and was grieved, thinking of Húrin as he bad seen him in the Nirnaeth Arnoediad, and the dreadful doom of his kin. As the Elves stood there, men came down from Nen Girith to look upon the Dragon, and when they saw to what end the life of Túrin Turambar had come they wept; and the Elves learning at last the reason of Túrin's words to them were aghast. Then Mablung said bitterly: "I also have been meshed in the doom of the Children of Húrin, and thus with words have slain one that I loved."
Then they lifted up Túrin, and saw that his sword was broken asunder. So passed all that he possessed.

(UT, Harn i Hín Hürin)

There he drew forth his sword, that now alone remained to him of all his possessions, and he said: 'Hail Gurthang! No lord or loyalty dost thou know, save the hand that wieldeth thee. From no blood wilt thou shrink. Wilt thou therefore take Túrin Turambar, wilt thou slay me swiftly?'
And from the blade rang a cold voice in answer: 'Yea, I will drink thy blood gladly, that so I may forget the blood of Beleg my master, and the blood of Brandir slain unjustly. I will slay thee swiftly.'
Then Túrin set the hilts upon the ground, and cast himself upon the point of Gurthang, and the black blade took his life. But Mablung and the Elves came and looked on the shape of Glaurung lying dead, and upon the body of Túrin, and they grieved; and when Men of Brethil came thither, and they learned the reasons of Túrin's madness and death, they were aghast; and Mablung said bitterly: 'I also have been meshed in the doom of the Children of Húrin, and thus with my tidings have slain one that I loved.'

Then they lifted up Túrin, and found that Gurthang had broken asunder. But Elves and Men gathered there great store of wood, and they made a mighty burning, and the Dragon was consumed to ashes. Túrin they laid in a high mound where he had fallen, and the shards of Gurthang were laid beside him.

(Silm, Chapter 21, Of Türin Turambar)

Gurthang - 'Iron of Death', name of Beleg's sword Anglachel after it was reforged for Túrin in Nargothrond, and from which he was named Mormegil. 258, 262, 265-6, 273, 276-8

anga - 'iron', Sindarin ang, in Angainor, Angband, Anghabar, Anglachel, Angrist, Angrod, Anguirel, Gurthang; angren 'of iron' in Angrenost, plural engrin in Ered Engrin.

gurth - 'death' in Gurthang (see also Melkor in the Index).

(Silm, Appendix)