Characteristics of the salagrama-stones

http://www.gsbkerala.com/salagrama.htm

Moorthys from the Ahobila Matam's Silver Mantapam

http://ahobilaminformation.blogspot.com/2012/02/saalagramam-moorthys-from-ahobila.html

Altar

1000 / 60000 Shaligrams

http://srigaurangashram.in/shaligram.html
http://www.hknet.org.nz/sstp-HariPrasadKemka.html

FAQ

http://www.adityarudraksha.com/FAQ%20About%20Saligram.html

Ammonites / More

http://gwydir.demon.co.uk/jo/fossils/ammonite.htm
http://www.nhm.ac.uk/nature-online/earth/fossils/fossil-folklore/fossil_types/ammonites.htm

Broken

Khandita Sphutita Viina Vandi Dakdhya Tathi Va Cha 
Saligram Sialyatra Tatra Dosho Na Vidyate

Even if a Salagram is damaged or broken, all sila are good to worship

Source 

Shree Vishotara Purane Shree Saligram Sila-stotram