There are 6 weapons and 6 amulets made of Onyx:

Onyx Rocket Launcher Onyx Shotgun Onyx Marksman Rifle Onyx Assault Rifle Onyx Pistols Onyx Submachine Gun

Onyx Spirit of Khepri Onyx Spirit of Osiris Onyx Spirit of Ra Onyx Spirit of Sobek Onyx Spirit of Shen Onyx Spirit of Set