Orpiment is an unremarkable yellow stone found as small clusters in igneous extrusive layers. It is neither fire-safe nor magma-safe.
 In Real Life
Orpiment is an arsenic sulfide (as is realgar), and is extremely toxic in real life. It poses no health hazards in Dwarf Fortress, however – dwarves can consume food and drink stored in orpiment pots without harm.
another arsenic sulfide, comes from realgar