Calcite
= Calcite
{wiki}
<Calcite> is a crystalline form of <calcium carbonate>, $\mathrm{CaCO_3}$. Its structure differs from other calcium-carbonate polymorphs despite identical chemical composition.
<Calcite> is optically anisotropic: light propagation depends on direction and polarization relative to the crystal. Its familiar double-refraction effect connects macroscopic optical observations with an ordered atomic structure.