Pyrite - FeS₂

Named in antiquity from the Greek "pyr" (fire), because sparks flew from it when hit with another mineral or metal. Pyrite is the most common of the small group of iron sulfide minerals. Many metals an semimetals are reported in pyrite analyses; however, all are minor, and many are present as tiny inclusions (for examples, Au, Cu and Pb). Pyrite may form significant, but incomplete solid solution with its Ni-isomorph, vaesite (NiS₂), and with cattierite (CoS₂). The brassy-yellow metallic colour of pyrite has in many cases lead to people mistaking it for Gold, hence the common nickname "Fool's gold".

Optical Properties:
• Form: Square, triangular and hexagonal sections, also granular.
• Colour: opaque, in oblique reflected light brass-yellow.
• Alteration: weathers easily, altering to limonite, etc.
• Occurrence: Pyrite is a very common mineral, found in a wide variety of geological formations from sedimentary deposits to hydrothermal veins and as a constituent of metamorphic rocks.

Bibliography

• Bucher, K., & Grapes, R. (2011). Petrogenesis of metamorphic rocks. Springer Science & Business Media.
• Fossen, H. (2016). Structural geology. Cambridge University Press.
• Howie, R. A., Zussman, J., & Deer, W. (1992). An introduction to the rock-forming minerals (p. 696). Longman.
• Passchier, Cees W., Trouw, Rudolph A. J: Microtectonics (2005).
• Philpotts, A., & Ague, J. (2009). Principles of igneous and metamorphic petrology. Cambridge University Press.
• 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.
• Vernon, R. H. (2018). A practical guide to rock microstructure. Cambridge university press.

Photo
Pyrite crystals. Sesia Lanzo zone, Piedmont, italian Alps. PPL image, 10x (Field of view = 2mm)	Pyrite crystals. Sesia Lanzo zone, Piedmont, italian Alps. PPL image, 10x (Field of view = 2mm)	Twinned pyrite crystal. Sesia Lanzo zone, Piedmont, italian Alps. PPL image, 10x (Field of view = 2mm)
Pyrite crystals. Sesia Lanzo zone, Piedmont, italian Alps. PPL image, 10x (Field of view = 2mm)	Pyrite crystals. Sesia Lanzo zone, Piedmont, italian Alps. PPL image, 10x (Field of view = 2mm)	Pyrite crystal. Sesia Lanzo zone, Piedmont, italian Alps. PPL image, 10x (Field of view = 2mm)
Pyrite crystals. Sesia Lanzo zone, Piedmont, italian Alps. PPL image, 10x (Field of view = 2mm)	Pyrite crystal (triangular section). Sesia Lanzo zone, Piedmont, italian Alps. PPL image, 10x (Field of view = 2mm)	Pyrite crystal (triangular and square sections). Sesia Lanzo zone, Piedmont, italian Alps. PPL image, 10x (Field of view = 2mm)
Pyrite crystal (triangular and square sections). Sesia Lanzo zone, Piedmont, italian Alps. PPL image, 10x (Field of view = 2mm)	Pyrite with calcite strain fringes. Sesia Lanzo zone, Piedmont, italian Alps. PPL image, 10x (Field of view = 2mm)	Pyrite with calcite strain fringes. Sesia Lanzo zone, Piedmont, italian Alps. XPL image, 10x (Field of view = 2mm)
Pyrite crystal. Sesia Lanzo zone, Piedmont, italian Alps. PPL image, 10x (Field of view = 2mm)	Twinned pyrite crystal. Sesia Lanzo zone, Piedmont, italian Alps. PPL image, 10x (Field of view = 2mm)	Pyrite crystal. Sesia Lanzo zone, Piedmont, italian Alps. PPL image, 10x (Field of view = 2mm)
Pyrite crystal (triangular sections). Sesia Lanzo zone, Piedmont, italian Alps. PPL image, 10x (Field of view = 2mm)	Pyrite crystals. Sesia Lanzo zone, Piedmont, italian Alps. PPL image, 10x (Field of view = 2mm)	Pyrite crystals. Sesia Lanzo zone, Piedmont, italian Alps. PPL image, 10x (Field of view = 2mm)
Pyrite with quartz strain fringes. PPL image, 2x (Field of view = 7mm)	Pyrite with quartz strain fringes. XPL image, 2x (Field of view = 7mm)	Pyrite with quartz strain fringes. XPL (with Compensator plate) image, 2x (Field of view = 7mm)
Pyrite with quartz strain fringes. XPL image, 2x (Field of view = 7mm)	Pyrite with quartz strain fringes. XPL image, 2x (Field of view = 7mm)	Pyrite with quartz strain fringes. PPL image, 2x (Field of view = 7mm)

Metamorphic Minerals

Texture and Microstructure

Metamorphic Rocks

Pyrite - FeS2

Pyrite - FeS₂