Over time, orpiment will deteriorate into a powder. The process takes a long time, but exposure to light will accelerate it. Specimens should be stored in dark, enclosed containers. Color is orange-yellow to yellow. Luster is resinous to pearly Transparency crystals are translucent to transparent.
Cleavage is perfect in one direction producing flexible, non-elastic flakes.
Fracture is flaky. Hardness is 1.5-2. Specific Gravity is 3.5 Streak is yellow Associated Minerals realgar , calcite , stibnite , barite and gypsum . Also usually has a distinct odor similar to sulfur, but is due to the arsenic. Best Field Indicators are crystal habit, cleavage, odor and color.