While comparing Opal and Grossular Garnet 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 Grossular Garnet chemical formula.
Another important criteria for qualitative analysis of gemstones is Opal and Grossular Garnet Specific gravity. Specific gravity is the relative density of a gemstone compared with respect to density of water. Gemologists use Opal and Grossular Garnet Optical Properties during the identification of gemstone. Specific gravity of Opal is 3.6 whereas that of Grossular Garnet is 3.6.