While comparing Leucite and Onyx 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 Leucite and Onyx chemical formula.
Another important criteria for qualitative analysis of gemstones is Leucite and Onyx Specific gravity. Specific gravity is the relative density of a gemstone compared with respect to density of water. Gemologists use Leucite and Onyx Optical Properties during the identification of gemstone. Specific gravity of Leucite is 2.55-2.70 whereas that of Onyx is 2.55-2.70.