Herapathite
Herapathite, or iodoquinine sulfate, is a chemical compound whose crystals are dichroic and thus can be used for polarizing light. The composition of herapathite has been shown by the danish chemist Sophus Mads Jørgensen in 1877 and others to be 4CH2·3SO4·2I3·6H2O, where C denotes the quinine molecule C20H24N2O2. The crystal can give up at least some of its water without losing its form and optical properties.