Parts of this story can be found in the Prose Edda and in the Poetic Edda.

Freya, beautiful, blue-eyed, blond goddess of love, beauty, and fertility had a weakness for beautiful jewels. She was wed to handsome Odur, the sunshine, and bore him two lovely daughters. They lived in her palace, Folkvanger, in the land of Asgard. One day Freya was out for a walk along the border of her kingdom. This was the boundary of the kingdom of the Black Dwarfs. As she walked she noticed some of the dwarfs making a beautiful necklace. It glistened as golden as the bright sun and caused Freya to stop to admire it. Freya was told this treasure was the Brisingamen, or the Brising necklace and of great value to the dwarfs.
"Oh, you must sell me the necklace. I will give a treasure of silver for I cannot live without it. I have never seen one as beautiful."
The dwarfs told her that all the silver in the world could not purchase the Brisingamen. Believing she could not endure without owning the necklace, she asked:
"Is there any treasure in the world for which you would sell me the necklace?"
"Yes, you must buy it from each of us." answered the dwarfs, "for it is the treasure of your love. If you are wed to each of us for a day and a night, Brisingamen shall be yours."
Bewitched by the sparkle of the beautiful necklace, Freya was over come with madness. She forgot Odur, she forgot her two lovely daughters, she even forgot she was the Queen of the Aesir. In her madness, she agreed to the pact. No one in Aesir knew about the weddings of barter except the mischief-maker Loki, who seemed to always be around when evil was brewing.
After four days and nights of these unholy unions, Freya returned to her palace to live in shame. She hid the necklace she had given her honor for. But Loki came to Odur in inform him of what had taken place in the land of the dwarfs. Odur demanded proof of these scandalous tales. To provide evidence, Loki set out to steal the necklace. Turning himself into a flea, he flew into Freya's chambers and bit her on the cheek while she slept. The bite caused Freya to turn so he was able to remove the necklace.
Loki went to Odur and showed him the evidence of her infidelity. Odur tossed the necklace aside, left the kingdom of Asgard, a traveled to far distant lands. Freya woke the next morning to find both her necklace and husband gone.
Weeping, she went to Valhalla to confess to the father god Odin whose palace was near the amber valley of Glaesisvellir. At the entrance to Valhalla was an amber grove called Glaeser, with trees that dripped beads of amber. The kindly Odin forgave Freya for her evil, but demanded a penance. Taking the Brisingamen from Loki, he commanded Freya to wear the necklace for eternity and wander the world in search of her lost love, Odur.
As she wanders the world she continues weeping. The teardrops which land on soil turn to gold in the rocks, those which fall in the sea are turned to amber.
The necklace was said to be an emblem of the stars or of the fruitfulness of the earth. The necklace enhanced Freya's beauty so much that she wore it day and night. According to some sources, it came to be so well associated with her that when Hymir stole Mjollnir, Freya loaned the necklace to Thor to complete his costume. (See The Theft of Thor's Hammer for more.)