While comparing Opal and Aragonite 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 Opal and Aragonite chemical formula.
Another important criteria for qualitative analysis of gemstones is Opal and Aragonite Specific gravity. Specific gravity is the relative density of a gemstone compared with respect to density of water. Gemologists use Opal and Aragonite Optical Properties during the identification of gemstone. Specific gravity of Opal is 2.93-2.96 whereas that of Aragonite is 2.93-2.96.