While comparing Benitoite and Alexandrite 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 Benitoite and Alexandrite chemical formula.
Another important criteria for qualitative analysis of gemstones is Benitoite and Alexandrite Specific gravity. Specific gravity is the relative density of a gemstone compared with respect to density of water. Gemologists use Benitoite and Alexandrite Optical Properties during the identification of gemstone. Specific gravity of Benitoite is 3.69-3.81 whereas that of Alexandrite is 3.69-3.81.