The speciality is that the Salagrama itself is considered a form of the Lord (Bhagavat Svarupam). There is no rule that it must be offered. The Lord is always present in the sanctum as Salagrama Perumal; we can say He Himself has taken the form of an ornament. I am not aware of any specific restrictive rules. However, one important thing: you should not drill holes in the Salagrama to make a necklace. Instead, the Salagrama should be encased or bound with silver or gold wire. Elders say that drilling a hole is an offence (apacaram). It is not that a Salagrama necklace is extremely “special” in a unique way; rather, worshipping the Salagrama itself (Tiruvaradhanam) is what is most significant. There is no fault in offering a Salagrama necklace to the Lord, and it can be viewed with wonder and devotion. Previous SUDARSANAM Questions and Answers