Loellingite is a mineral that belongs to the pyrite group, and it's mainly composed of iron and arsenic. This mineral is commonly found in hydrothermal veins and pegmatites, and it's used in the manufacturing of steel alloys and pigments. Loellingite is also known by several other synonyms like arsenopyrite, arsenical pyrite, arsenical iron, and FeAs2. However, it's worth mentioning that some of these synonyms describe mineral formations that are similar to loellingite but have slightly different chemical compositions or crystal structures. Nevertheless, loellingite remains a valuable mineral resource for various industrial applications, and its synonyms provide a convenient term bank for mineralogists and geologists.