STORY OF SHYAMANTAKA MANI (GEM) :
Satrajit is an ardent devotee of Sun God, the Sun God pleased with his devotion, he appeared before him and presented Syamantaka Mani (gem) which produces about 170 pounds of gold every day. Once Lord Krishna asked Satrajit to present Shyamantaka mani to his grand father Ugrasena, because of that gem the whole world could benefit. But Satrajit refused. Prasena brother of Satrajit, one day, Prasena decided to wear the gem when he went hunting. He was killed by a lion. Jambavanth killed the lion and took the jewel away to his cave.
Jambavanth is the great devotee of Lord Rama, he did not care much for the gem as such. He only wanted to present it to his son as a toy. In meanwhile Prasena did not return, Satrajit falsely accused Lord Krishna of killing Prasena for the sake of the jewel. Lord Krishna, in order to remove the stain on his reputation, set out in search of the jewel and found it in Jambavantha's cave, with his child. Jambavantha attacked Lord Krishna thinking him to be an intruder who had came to take away the jewel. They fought each other 28 days. Jambavan knew that only his Lord Rama has the capacity to beat him. Jambavantha gave Krishna the jewel and his daughter Jambavati in marriage. Lord Krishna returned to Dwaraka with Jambavthi and the jewel, Lord Krishna returned jewel to Satrajit, who in turn repented for his false accusation. He promptly offered to give Krishna the jewel and his daughter Satyabhama in marriage. Lord Krishna accepted Satyabhama as his wife but did not accept the jewel.