1. Is Saligrama in the form of black stone only ?

Yes. Mostly black stone only. Reddish black are also there, but they are very rare. Red Saligrama are not worshipped in houses.

2. Is it available at gandaki river in nepal only or else where also ?

In gandaki river only.

3. Does it have the symbol of sudarshana chakra or other holy weapons of lord vishnu?

Chakra symbol only. No other symbols.

4. Is it a naturall formation or impression of any river worm or insect due to passage on the black stone or it used as a shell by the insect ?

It is not a stone-formation by nature. The chakras on the stones are formed by the river worms called Vajra-keeta. Its teeth/nails are said to be harder than granite stone. The chakra formation is found not only on the outer surface of the Saligrama.

There are chakras inside Saligrama also. This can be seen through the hole or holes on the Saligrama with the aid of torch light. The holes are termed as vadana (mouth). Chakras can be seen inside these holes. At the very face of this chakra one can confirm or suspect whether a particular Saligrama is original or duplicate.

The Vajra keeta worms drill the stones, get inside and live there. During their stay inside the stones, they cause these chakras. Similarly outside Chakras also are caused by the worms only. Saligrama are used as living place by the worms not used as shells.

The puranic declaration is that the Lord Himself causes these chakras in the guise of worms. He reveals His presence in Saligrama through the Chakras. Because He is already present there by his own choice, We do not perform any pratishta-ritual for Saligrama just as we do for other idols.

There are also some normal size, small and very small size Saligramas with no hole and ni chakra. They look like mere black stones. But if you hold it against the lamp and look through the stone, you will be surpraised to find it is transparent. That is, the reddish light will be visible insid the stone. These Saligramas are called Ratna Garbha. They are very rare.

5. Is it a fact that more number of chakras in a Saligrama represnet its significance ?

No such significance. A Saligrama with one or two chakras is as powerful as the one with a dozen chakras. A Saligrama with 7 holes and 14 chakras is known as Ananta Padmanabha Murthy. 2 holes and 4 chakras is Narayana Murthy and so on. All the Murthys are of the same power.

6. Is it a coincidence of the availability at river Gandaki is not the abode of Shiva.

7. Any other mythological background to substantiate the prevalence of such stones deserve worship as the manifestation of Lord Vishnu ?

Of the 18 Puranas, a good number of them, under different contexts, proclaim the mahima of Saligrama as Vishnu pooja. They also proclaim that the White stones ashore at Dwaraka is as powerful as Saligrama. These white stones are called : "CHAKRANIKA". This is to be kept in pooja along with Saligrama, proclaims the Purana.

SALIGRAM SHILA YATRA, YATRA DHVARAVATHI SHILA |

UBAYO SANKHMO YATRA, YATRA MUKTHRNASAMSHAYAHA ||

8. Is any size prescribed for the worship in the daily puja by Madhwas? It is learnt that abnormal sizes should be kept in the Temples/Mutts etc.

Yes. The size recommended for the puja in the house is the smaller ones which can be accommodated in the closed fist. Abnormal ones are to be kept in the Temples/Mutts etc.

9. Is it true that Saligrama should not be kept in the house without daily Abusheka ?

The emphasis is only to stress the point that you should not be lazy and miss Saligrama Puja for too long a period on False excuses. It is not to ask you do away with Saligrama on grounds of imaginary problems.

10. Are Saligramas worshipped exclusively by Madhwas or by others also ?

Iyengars do Saligrama Puja as also some of the Vadama Iyers who wear Gopichandana.