Made

In kārttika-māhātmya of padma purāṇa there is a statement during the discourse between yama-dhūmrakeśa;

śailī dārumayī lauhī lepyā lekhyā ca saikatā |
manomayī maṇimayī śrī-mūrtir aṣṭadhā smṛtā||
śālagrāma-śilāyāṃ tu sākṣāt śrī-kṛṣṇa-sevanam |
nityaṃ saṃnihitas tatra vāsudevo jagad-guruḥ

1. Stone, 
2. wood, 
3. iron or metal, 
4. mud, 
5. picture, 
6. sand, 
7. mind and 
8. jewels 

are the eight ingredients that Deities can be made from in this world. The worship of Salagram Sila is the worship of Lord Hari directly. Jagat Guru, the spiritual master of the universe, Lord vāsudeva, eternally resides within śālagrām śilā.