Specimens Laurionite is a rare halide mineral. A polymorph is a mineral that shares the same exact chemistry with other minerals but has a different crystal structure. When there are just two minerals involved they are referred to as dimorphs. In the case of laurionite, its structure gives it an orthorhombic symmetry whereas paralaurionite has a monoclinic symmetry. Both minerals are found in lead slags at only a few localities in the world.
Slags are the debris left over from previous mining operations.
These slags are generally thought by the miners to be of such low grade ore that they are simply discarded. Often these slag piles are later reclaimed for their now more valuable metals by modern techniques that can extract profitable amounts of metal from these lower grade ores. Mineralogists often consider these slag piles to be valuable as collecting sites for rare and sometimes unknown minerals. Such is the case for laurionite and paralaurionite. Although both have been known for over a century, like them, many minerals were and are being discovered in lead slag piles, sometimes leftover from mining operations that stopped centuries before.