1) Monoclinic mineral 
Spurrite is a white, yellow or light blue mineral with monoclinic crystals. Its chemical formula is Ca5(SiO4)2CO3. Spurrite is generally formed in contact metamorphism zones as mafic magmas are intruded into carbonate rocks. Spurrite`s space group is P 2/a. It is biaxial with a birefringence of 0.0390–0.0400, giving second order red interferenc....