Omphacite is the solid solution of Fe-bearing diopside (CaMgSi2O6) and jadeite (NaAlSi2O6). Depending on how much the coupled substitution of (Na, Al)-(Mg-Fe, Ca) happens, the chemical composition of omphacite varies continuously from pure diopside to pure jadeite.[1] Due to the relatively small radius of (Na, Al) atoms, the unit cell volume linearly decreases as jadeite component increases.[12] In addition, the coupled substitution also stiffens the crystals.