If you ever happened to have a look inside a Vaishnavite's Pooja room, you might have had a glimpse of a black stone called Saligramam being worshipped. It is usually black in color with the symbol of sudarshana chakra. The chakras can be seen both outside and inside. The Saligrama stone is not believed to be just another stone found in the nature. It is found only at Gandaki River situated high in the Himalayas in Nepal. It is believed that the chakra symbols are formed by river worms called Vajra Keeta. It is believed that these worms drill the stones, get inside and use the stones a dwelling place.
There is a legend behind the origin of Saligramam. Once upon a time, Lord Siva was waging a war with an asura called Jallundhara. The war seemed to be between two equals and not just another war of a God with a demon. It was in fact a test of chastity of their consorts. (It is a Hindu belief that chastity of the wife protects her husband even from death) Lord Siva knew that unless the chastity of Vrinda, Jallundhara's wife is spoiled, he cannot be killed as he will be protected by the power of her chastity. But it was against the nature of Gods to indulge in a heinous act like spoiling a woman's chastity.
But there was no such taboo for the demon Jallundhara. He thought that by spoiling the chastity of Goddess Parvati he could defeat Lord Siva. But Goddess Parvati could see through Jallundhara's trick and ended his guise. She signaled Lord Krishna (Avatara of Lord Vishnu) that it was now just to spoil the chastity of Jallundhara's wife and it will not be a sin. Lord Krishna approached Vrinda in the guise of Jallundhana. She could not understand that it is not her husband and lost her chastity.
Later when she came to know about this, she cursed Lord Vishnu to turn into grass, stone, tree and plant. It is believed that Kusha-grass, Saligram-stone, Pipal-tree and Tulsi-plant are incarnations of Lord Vishnu and worshipped henceforth. (There is another version of the story for the origin of Tulsi and Saligrama shila which will be posted later.)
Padma purana states that resident of a salagrama is Lord Kesava himself and along with him reside all the devatas, asuaras, yaksas and the fourteen worlds. Hence, giving a salagrama, is the best form of charity. It also states that Lord Siva himself stays in the salagrama sila and hence worshipping it is of importance to both Vaishnavites and Saivites. Even if a salagrama is cracked, split, or broken it will have no harmful effect if it is worshiped with attention and love by a devotee. Gautamiya Tantra states that merely by touching a shalagrama one becomes freed from the sins of millions of births. In Skanda purana, it is said that that any person who has seen salagrama stone, paid obeisances to it, bathed and worshipped it, has achieved the results of performing ten million sacrifices and giving ten million cows in charity. According to Garuda Purana, The Lord resides in many places in which he may be worshipped, but of all the places Salagrama is the best.