High Quality Content by WIKIPEDIA articles! 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 interference colors when viewed under crossed polarizers in a petrographic microscope. The calcium is in six-fold coordination with the oxygen, the silicon is in a four-fold coordination with the oxygen and the carbon is in two-fold coordination. One unique characteristic of spurrite is that it actually abides by two twin laws. Polysynthetic twinning can occur along its (001) and another type of twinning can occur parallel to its optical axes.

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