Orpiment - As₂S₃

Orpiment, As₂S₃, is a common monoclinic arsenic sulfide mineral. Orpiment is an orange to yellow mineral that is found worldwide, and occurs as a sublimation product in volcanic fumaroles, low temperature hydrothermal veins, hot springs and as a byproduct of the decay of another arsenic mineral, realgar. It is often found in association with realgar. It takes its name from the Latin auripigmentum (aurum = gold + pigmentum = pigment) because of its deep yellow color.

Optical properties:
• Cleavage: (010) Perfect.
• Color: Lemon yellow, Brownish yellow, Orange yellow.
• Habit: Foliated - Two dimensional platy forms; Massive - Fibrous - Distinctly fibrous fine-grained forms.

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Panoramic view of orpiment thin section. Image by Andy Tindle (Virtual Microscope). PPL image, field of view = 2.5cm.

Panoramic view of orpiment thin section. Image by Andy Tindle (Virtual Microscope). XPL image, field of view = 2.5cm.

Bibliography

• Cox et al. (1979): The Interpretation of Igneous Rocks, George Allen and Unwin, London.
• Howie, R. A., Zussman, J., & Deer, W. (1992). An introduction to the rock-forming minerals (p. 696). Longman.
• Le Maitre, R. W., Streckeisen, A., Zanettin, B., Le Bas, M. J., Bonin, B., Bateman, P., & Lameyre, J. (2002). Igneous rocks. A classification and glossary of terms, 2. Cambridge University Press.
• Middlemost, E. A. (1986). Magmas and magmatic rocks: an introduction to igneous petrology.
• Shelley, D. (1993). Igneous and metamorphic rocks under the microscope: classification, textures, microstructures and mineral preferred-orientations.
• Vernon, R. H. & Clarke, G. L. (2008): Principles of Metamorphic Petrology. Cambridge University Press.

Photo
Lamellar orpiment crystals, Bagnore (Grosseto, Italy). PPL image, 2x (Field of view = 7mm)	Lamellar orpiment crystals, Bagnore (Grosseto, Italy). PPL image, 2x (Field of view = 7mm)	Lamellar orpiment crystals, Bagnore (Grosseto, Italy). PPL image, 2x (Field of view = 7mm)
Lamellar orpiment crystals, Bagnore (Grosseto, Italy). PPL image, 2x (Field of view = 7mm)	Lamellar orpiment crystals, Bagnore (Grosseto, Italy). PPL image, 2x (Field of view = 7mm)	Lamellar orpiment crystals, Bagnore (Grosseto, Italy). PPL image, 2x (Field of view = 7mm)
Lamellar orpiment crystals, Bagnore (Grosseto, Italy). PPL image, 2x (Field of view = 7mm)	Lamellar orpiment crystals, Bagnore (Grosseto, Italy). PPL image, 2x (Field of view = 7mm)	Lamellar orpiment crystals, Bagnore (Grosseto, Italy). PPL image, 2x (Field of view = 7mm)