While comparing Allanite and Idocrase 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 Allanite and Idocrase chemical formula.
Another important criteria for qualitative analysis of gemstones is Allanite and Idocrase Specific gravity. Specific gravity is the relative density of a gemstone compared with respect to density of water. Gemologists use Allanite and Idocrase Optical Properties during the identification of gemstone. Specific gravity of Allanite is Not Available whereas that of Idocrase is Not Available.