While comparing Obsidian and Ammonite physical properties, the important data you should know is its chemical composition. Since chemical formula defines the molecular structure of the crystal, most of the physical properties like color, tenacity, solubility are governed by Obsidian and Ammonite chemical formula.
Another important criteria for qualitative analysis of gemstones is Obsidian and Ammonite Specific gravity. Specific gravity is the relative density of a gemstone compared with respect to density of water. Gemologists use Obsidian and Ammonite Optical Properties during the identification of gemstone. Specific gravity of Obsidian is Not Available whereas that of Ammonite is Not Available.