Shaastra say that bones are impure but Shankh are super pure. Shankh (conch) has a very special and important place in our religious lives. It has been regarded very holy and is used in worship. The Sanskrit word Shankh has the etymological meaning of pacifying the inauspicious (Unadi-Sootra, 1:104, ‘samyati ashubham asmat’). It is most characteristically associated with Vishnu, and is one of the four of His Aayudh (literally ‘weapon’, but employed in the sense of whatever is held in the hand) usually found in his hands; the discus (Chakra), the mace (Gadaa) and the lotus (Padma) being the other three. Normally it is considered the house of some animal when he leaves his house, his house is collected.
Uses of Shankh
How do we use Shankh?
--When an Aaratee of God is performed in an house or in a temple, Shankh is blown.
--There are some Shankh which are good even for worshiping, such as Lakshmee Shankh.
--When something is begun, a Shankh is blown to indicate the start of that event.
--In Mahaabhaarat war Mahaarathee had their own Shankh and they were identified by those Shankh, such as Krishn by His Paanchjanya Shankh, Arjun by his Devdatt Shankh etc.
--In Mahaabhaarat, when Duryodhan wanted to identify Paandav in Viraat's kingdom, he attacked Viraat's kingdom. And when Arjun proceeded to fight with them with Uttar, Kaurav could not recognize him. But when he blew his Devdatt Shankh, they recognized him by his Shankh only.
--Mahaabhaarat war used to begin and end with the blow of Shankh.
How Shakh Came on Prithvi?
Its story goes like this that there was a Vishnu's Paaarshad (personal guard) named Sudaamaa in Gau Lok. Once Raadhaa cursed him to be born on Prithvi, so he was born on Prithvi as Shankhchood Asur. He was very mighty. Above that he obtained an armor too from Brahmaa Jee after a severe penance. The armor was that till his wife will be chaste to him he will not be hurt by anybody. Now he became fearless and he started tormenting people in Tri-Lok. His wife Tulasee was a very Pativrataa woman, so he was safe
Seeing his atrocities, Devtaa went to Brahmaa Jee to request him to kill Shankhchood, and Brahmaa Jee went to Vishnu. Vishnu planned to kill him this way that, He sent Shiv to fight with Shankhchood, and He himself went to Tulasee in disguise of Shankhchood and asked for her favor to be with Him. Tulasee yielded to his desire. As she came to know that he was not her husband but was Vishnu she filled with rage. Since Vishnu broke her Paativrat Dharm, she cursed Him in frustration to be a black stone. Vishnu accepted her curse, and said - "I accept your curse. You did what you should have done, now I will do what I should do. My Darshan does not go waste, so I grant you the boon that you will become a River (Gandakae River) and I will live in your heart in the form of stone (Shaalgraam). Besides, your hair will be grown as Tulasee plant and I will not accept any food without you. Even your husband's bones will appear on Prithvi as conch and they will be considered holy and will be used in my worship.
Asur With the Body of Shankh
There are a couple of Asur also who had the body of Shankh - they were Panchjan and Shankhaasur.
(1) Panchjan Asur lived in Sea and was killed by Krishn when He was looking for His Guru's son to pay His Guru Dakshinaa to him. After killing him he took his body (Shankh) and kept is it with Him. Even today whatever Shankh you see in His hand is the same. Coming from Panchjan's body, its name is Paanchjanya Shankh.
(2) Another Asur was Shankhaasur. His body was also of Shankh. He was the son of Samudra (Sea). he had stolen Ved, so Vishnu had to kill him and He asked Rishi to collect Ved Mantra from the Sea.
Some Famous Shankh
There are some famous and holy Shankh, such as - Lakshmee Shankh, known as Dakshinaavartee Shankh or Vallampuree Sanggu also (used in Abhishek and Aaratee), Vishnu Shankh; Heeraa Shankh or Pahaadee Shankh - it attracts wealth; etc.