Realgar and orpiment are near similar minerals, both arsenic sulphides, both belonging to the monoclinic crystal system. They form in hydrothermal veins and around volcanic hot springs, where its crystals may sublimate from hot vapours. When fresh their colours range from yellow-orange to striking reds, but these fade slowly with time. They mostly occur as granular crusts, more rarely in the form of prismatic crystals or amorphous agglomerates. They have throughout history experienced extensive use as an ore of arsenic metal, as a pigment, a medicine and many other applications. Care is needed on account of the poisonous nature of both. The substrate here is crystalline quartz, interspersed with some pyrite. Actual width of sample is 100 mm, provenance is the Castrovirreyna mine, Huancavelica, Peru.