While comparing Sulphur and Nepheline 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 Sulphur and Nepheline chemical formula.
Another important criteria for qualitative analysis of gemstones is Sulphur and Nepheline Specific gravity. Specific gravity is the relative density of a gemstone compared with respect to density of water. Gemologists use Sulphur and Nepheline Optical Properties during the identification of gemstone. Specific gravity of Sulphur is 2.55-2.65 whereas that of Nepheline is 2.55-2.65.