It is believed (in Hindu Mythology) that Gods (Devas and Asuras), churned the ocean known as Samudra manthan to get Amrita (Devanagari - अमृत), fourteen treasures jewels ( Ratna ) emerged from the ocean. The fourth Ratna that was emerged is known as Kaustabh. It represents pure consciousness shining in all luminous manifestations.When this divine jewel came out of the ocean as the result of churning then it was said by Lord Shiva that nobody in the universe could handle the brilliance and magnificence of this "Mani" since it could corrupt the bearer by infusing in him/her its greed to carry it forever. But it was then decided that Lord Vishnu was the only person in the entire universe who could carry it without falling for its greed and henceforth this jewel was given to him. Since then it is believed that nobody including men, asuras, devas, yakshas, gandharvas, rakhshas etc. can carry it without getting corrupt except Lord Vishnu. Kaustubh is special type of divine jewel.