 Allanite and gadolinite are examples of minerals which have been claimed to exhibit true pyrognomic properties but have since been shown to exhibit thermoluminescence.The term was originally introduced by the German chemist and mineralogist Theodor Scheerer (1813-1873) in 1840, but the phenomenon had been previously observed by William Hyde Wollaston and Jöns Jacob Berzelius.The term is still used today to describe the thermoluminescence exhibited by various metamict minerals.