While comparing Hypersthene and Sillimanite 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 Hypersthene and Sillimanite chemical formula.
Another important criteria for qualitative analysis of gemstones is Hypersthene and Sillimanite Specific gravity. Specific gravity is the relative density of a gemstone compared with respect to density of water. Gemologists use Hypersthene and Sillimanite Optical Properties during the identification of gemstone. Specific gravity of Hypersthene is 3.20-3.26 whereas that of Sillimanite is 3.20-3.26.