The Shaligram is the most sacred stone worshipped by the Vaishnavas and is used to worship Vishnu .According to shastra worship Shree Shaligram for six values of life ;-
Righteous living, Wealth, Protection, good health, pleasures and Spiritual .
As per Gautamiya Tantra,
GANDAKYAS CAIVA DESE CA SALAGRAMA STHALAM MAHAT
PASANA TAD BHAVAM YAT TAT SALAGRAMAM ITI SMRTAM
(HARI BHAKTI VILASA 5/296 From GAUTAMIYA TANTRA )
Near the kali - Gandaki river, there place called Dhamoder kunda.The stones which appear in that place are called shalagram shila. According to the Hindu tradition this stone is the shelter for a small insect known as "Vajra-Keeta" that has a diamond tooth which cuts through the Shaligram stone and stays inside it. The Saligram stones are hundreds of million years old when the Himalaya was an ocean floor. The marks on the Shaligram gives it a special significance , the Discus of Lord Vishnu. The Shaligrams come in different colours, such as red, blue, black. All the varities are considered very sacred. The Shaligrams of different shapes are often associated with different incarnations of Lord Vishnu .
According to the Vaishnavas the Shaligram is the "dwelling place of Lord Vishnu" and any one who keeps it, must worship it daily. The Lord Krishna himself mentions the qualities of Shaligram to 'Yudhishtra' in the Mahabharta. Most of the Shaligrams are considered auspicious, some are very sacred, while others are considered to bring good luck, money, peace and so on.
Scientifically The Shaligrams are basically described as fossil-stones and characterized by the presence of discus marks. Shaligram-stones (black stones in which fossil ammonites are embedded) are the most celebrated universally. Worship of these stones is widespread and dates back to a distant past. They are worshipped in temples, monasteries and households all over the world, as visible and natural emblems of Vishnu. They are also worshipped in quasi-religious functions like house-warming (grha-pravesa, vastu-puja), pacificatory rites of different sorts (santi), marriages and funerary rituals.
The legend, related at length tells us that Lord Vishnu for benefit of mankind in kaliyuga comes in earth in the form of Shaligram and in tulsi tree. Like the worship of Shiva in the form of a Linga, the worship of Vishnu in the shape of a Shaligram, is aniconic in character.
In the worship of Shaligrams, no initiation is required; there is no special hymnology or specific procedure of worship, nor any need for a qualified priest or master of ceremonies. Worshipped by regular bathing saligram stones in curds, ghee, milk or water will give untold merit and will bestow all the benefits.
Saligram-stones are found only in the river Gandaki, which is a Himalayan stream, celebrated since antiquity as Narayani, Saligrami, Hiranvati and Hiranyavati. The epic Mahabharata speaks of its sanctity (Bhishma-Parva). The Puranas also describe it as a sacred stream in which all the gods and titans abide. By merely looking at it, one would eliminate all his mental dement’s, by touching it his bodily sins are burnt , and by sipping its water the verbal demerits are destroyed. One who comes into contact with this sacred stream will be liberated from the cycle of birth and deaths, even if he be a sinner.
There is a lake at the source of the Kali-Gandaki, called Damodar-Kunda at Nepal. The lower Gandaki is well known as Mukti-Natha-Kshetra, also called Saligrama-Kshetra. The sacred stones are largely found on the banks of Kali-Gandaki . Damodara-Kunda is a Saivite place of pilgrimage. These spots where saligrama-stones are found located within the Nepal territory.
Whether one has real devotion or not, if he worships a saligrama-stone with prostration before it, he will surely get emancipated from the cycle of phenomenal existence. The person who offers a daily service for the saligrama stone will be freed from the fear of death, and he will cross over the stream of births and deaths.
According to the religious text of Devi Bhagwate (and other scriptures) to kill demon Jalandhar Lord Vishnu have to destroy wife Brindha's sati dharma. When he did that Sati Brindha gave four seeming desecrations to Lord Vishnu to become stone, grass, tree, plant. To wash away this reaction Lord Vishnu took four avatars (incarnations). He became stone (Sri Saligram) grass (Kush) tree (Pipal) and plant (Tulsi). from this time onwardse the Saligrams are considered to be most auspicious to behold and to worship. As per Skanda Purana there can never be a price put on any Shaligram as there is not enough gold, jewels or any precious thing exist in the world to equal even a single Shaligram. We accept a small donation to cover the cost of the wages, lodging, boarding and potter / transportation charges paid to the poor villagers who collect and bring them to us. These villagers risk their life in search of rare Shaligrams under very difficult and trying climatic conditions that exist in and around Kali Gandaki river at Muktinath (Himalayas Nepal) to bring these auspicious Shaligrams to all of us.
As per Skanda Purana, Padma Purana and other epics, the worshipper of Shree Shaligram is blessed to attain all desirable things, worldly comforts, good wife, good sons, good health, immense wealth, peaceful environment prevails in his surroundings and he gets immense protection against all evil forces. His all anxieties, mental tension goes off and all ambitions are fulfilled . Even the water that has just touched the Shaligram Shila becomes “Amrit” and by drinking it "man" is relived of all diseases. Worshipping of Shaligram helps in meditation and attainment of spiritual liberation.
Besides the accounts found in several puranas (like Brahma-vaivarta, Agni, Padma, Garuda, Nrsimha, Skanda, Brahma and Brahmanda) there are scripture like Shalagram-mahatmya included in Gautamiya-tantra, Shalagram-pariksha in Magh-mahatmya section of the Padma purana, Puja-prayog, Haribhaktivilas of Gopal Bhatta, Shalagramarchana-chandrika, Puja-pankaja-bhaskara, Shalagram-mimamsa of Somanatha-vyasa and more......
Most puranas advocates that the worship of Salagramas as capable of producing material benefits like wealth, progeny, success, long life, cattle, celebrity, health and so on
"aputro labhate putram salagrama-pujanat"