For Fëanor, being come to his full might, was filled with a new thought, or it may be that some shadow of foreknowledge came to him of the doom that drew near; and he pondered how the light of the Trees, the glory of the Blessed Realm, might be preserved imperishable. Then he began a long and secret labour, and he summoned all his lore, and his power, and his subtle skill; and at the end of all he made the Silmarils.
As three great Jewels they were in form. But not until the End, when Fëanor shall return who perished ere the Sun was made, and sits now in the Halls of Awaiting and comes no more among his kin; not until the Sun passes and the Moon falls, shall it be known of what substance they were made. Like the crystal of diamonds it appeared, and yet was more strong than adamant, so that no violence could mar it or break it within the Kingdom of Arda. Yet that crystal was to the Silmarils but as is the body to the Children of Ilúvatar: the house of its inner fire, that is within it and yet in all parts of it, and is its life. And the inner fire of the Silmarils Fëanor made of the blended light of the Trees of Valinor, which lives in them yet, though the Trees have long withered and shine no more. Therefore even in the darkness of the deepest treasury the Silmarils of their own radiance shone like the stars of Varda; and yet, as were they indeed living things, they rejoiced in light and received it and gave it back in hues more marvellous than before.
All who dwelt in Aman were filled with wonder and delight at the work of Fëanor. And Varda hallowed the Silmarils, so that thereafter no mortal flesh, nor hands unclean, nor anything of evil will might touch them, but it was scorched and withered; and Mandos foretold that the fates of Arda, earth, sea, and air, lay locked within them.

(Silm, Chapter 7, Of the Silmarils and the Unrest of the Noldor)

Even among the Eldar she [Galadriel] was accounted beautiful, and her hair was held a marvel unmatched. It was golden like the hair of her father and of her foremother Indis, but richer and more radiant, for its gold was touched by some memory of the starlike silver of her mother; and the Eldar said that the light of the Two Trees, Laurelin and Telperion, had been snared in her tresses. Many thought that this saying first gave to Fëanor the thought of imprisoning and blending the light of the Trees that later took shape in his hands as the Silmarils. For Fëanor beheld the hair of Galadriel with wonder and delight.

(UT, THE HISTORY OF GALADRIEL AND CELEBORN)

In his right hand Morgoth held close the Silmarils, and though they were locked in a crystal casket, they had begun to bum him, and his hand was clenched in pain; but he would not open it.
...
Morgoth forged for himself a great crown of iron, and he called himself King of the World. In token of this he set the Silmarils in his crown. His hands were burned black by the touch of those hallowed jewels, and black they remained ever after; nor was he ever free from the pain of the burning, and the anger of the pain.

(Silm, Chapter 9, Of the Flight of the Noldor)

Then suddenly she eluded his sight, and out of the shadows began a song of such surpassing loveliness, and of such blinding power, that he listened perforce; and a blindness came upon him, as his eyes roamed to and fro, seeking her.
All his court were cast down in slumber, and all the fires faded and were quench ed; but the Silmarils in the crown on Morgoth's head blazed forth suddenly with a radiance of white flame; and the burden of that crown and of the jewels bowed down his head, as though the world were set upon it, laden with a weight of care, of fear, and of desire, that even the will of Morgoth could not support.
...
Then he drew forth the knife Angrist; and from the iron claws that held it he cut a Silmaril. As he closed it in his hand, the radiance welled through his living flesh, and h is hand became as a shining lamp; but the jewel suffered his touch and hurt him not. It came then into Beren's mind that he would go beyond his vow, and bear out of Angband all three of the Jewels of Fëanor; but such was not the doom of the Silmarils.

(Silm, Chapter 19, Of Beren and Lúthien)

Lúthien was spent, and she had not time nor strength to quell the wolf. But Beren strode forth before her, and in his right hand he held aloft the Silmaril. Carcharoth halted, and for a moment was afraid. 'Get you gone, and fly!' cried Beren; 'for here is a fire that shall consume you, and all evil things.' And he thrust the Silmaril before the eyes of the wolf.
But Carcharoth looked upon that holy jewel and was not daunted, and the devouring spirit within him awoke to sudden fire; and gaping he took suddenly the hand within his jaws, and he bit it off at the wrist. Then swiftly all his inwards were filled with a flame of anguish, and the Silmaril seared his accursed flesh. Howling he led before them, and the walls of the valley of the Gate echoes with the clamour of his torment.
So terrible did he become in his madness that all the creatures of Morgoth that abode in that valley, or were upon any of the roads that led thither, fled far away' for he slew all living things that stood in his path, and burst from the North with ruin upon the world. Of all the terrors that came ever into Beleriand ere Angband's fall the madness of Carcharoth was the most dreadful; for the power of the Silmaril was hidden within him.

(Silm, Chapter 19, Of Beren and Lúthien)

At that very time great craftsmen of Nogrod were lately come into Doriath; and the King therefore summoning them declared his desire, that if their skill were great enough they should remake the Nauglamír, and in it set the Silmaril. Then the Dwarves looked upon the work of their fathers, and they beheld with wonder the shining jewel of Fëanor; and they were filled with a great lust to possess them, and carry them off to their far homes in the mountains. But they dissembled their mind, and consented to the task.
Long was their labour; and Thingol went down alone to their deep smithies, and sat ever among them as they worked. In time his desire was achieved, and the greatest of the works of Elves and Dwarves were brought together and made one; and its beauty was very great, for now the countless jewels of the Nauglamír did reflect and cast abroad in marvellous hues the light of the Silmaril amidmost.

(Silm, Chapter 22, Of the Ruin of Doriath)

Then Elwing and the people of Sirion would not yield the jewel which Beren had won and Luthien had worn, and for which Dior the fair was slain; and least of all while Earendil their lord was on the sea, for it seemed to them that in the Silmaril lay the healing and the blessing that had come upon their houses and their ships. And so there came to pass the last and cruellest of the slayings of Elf by Elf; and that was the third of the great wrongs achieved by the accursed oath.

(Silm, Chapter 24, Of the Voyage of Eärendil and the War of Wrath)

Then such few of that people as did not perish in the assault joined themselves to Gil-galad, and went with him to Balar; and they told that Elros and Elrond were taken captive, but Elwing with the Silmaril upon her breast had cast herself into the sea. Thus Maedhros and Maglor gained not the jewel; but it was not lost. For Ulmo bore up Elwing out of the waves, and he gave her the likeness of a great white bird, and upon her breast there shone as a star the Silmaril, as she flew over the water to seek Eärendil her beloved.
...
Yet Eärendil saw now no hope left in the lands of Middle-earth, and he turned again in despair and came not home, but sought back once more to Valinor with Elwing at his side. He stood now most often at the prow of Vingilot, and the Silmaril was bound upon his brow; and ever its light grew greater as they drew into the West. And the wise have said that it was by reason of the power of that holy jewel that they came in time to waters that no vessels save those of the Teleri had known;..

(Silm, Chapter 24, Of the Voyage of Eärendil and the War of Wrath)

But the jewel burned the hand of Maedhros in pain unbearable; and he perceived that it was as Eonwe had said, and that his right thereto had become void, and that the oath was vain. And being in anguish and despair he cast himself into a gaping chasm filled with fire, and so ended; and the Silmaril that he bore was taken into the bosom of the Earth. And it is told of Maglor that he could not endure the pain with which the Silmaril tormented him; and he cast it at last into the Sea, and thereafter he wandered ever upon the shores, singing in pain and regret beside the waves. For Maglor was mighty among the singers of old, named only after Daeron of Doriath; but he came never back among the people of the Elves. And thus it came to pass that the Silmarils found their long homes: one in the airs of heaven, and one in the fires of the heart of the world, and one in the deep waters.

(Silm, Chapter 24, Of the Voyage of Eärendil and the War of Wrath)