Saussurite

Saussurite is a mineral aggregate which is formed as a hydrothermal alteration product of plagioclase feldspar.It was named after the Swiss explorer Horace Benedict de Saussure, who discovered it on the slopes of Mont Blanc. It’s a common alteration product of plagioclase and its require addition of water, that change An-component to epidote (Zoisite or Clinozoisite), ancd the residual plagioclase is left as albite. Saussurite is formed under the same condition that characterize the greenschist or other low-P facies. Saussurite is not however recognized as a true mineral because it is a microscopic mixture of several other minerals, zoisite, epidote, sericite, albite.

Light green saussurite and dark green alered olivina. Allalin Glacier, Zermatt-Saas, Svizzera. From e-rocks

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
Plagioclase altered by saussurite. XPL image, 10x (Field of view = 2mm)	Plagioclase altered by saussurite. XPL image, 10x (Field of view = 2mm)	Plagioclase altered by saussurite. PPL image, 10x (Field of view = 2mm)
Plagioclase altered by saussurite. XPL image, 10x (Field of view = 2mm)	Plagioclase altered by saussurite. PPL image, 10x (Field of view = 2mm)	Plagioclase altered by saussurite. XPL image, 10x (Field of view = 2mm)
Plagioclase altered by saussurite. PPL image, 10x (Field of view = 2mm)	Plagioclase altered by saussurite. XPL image, 10x (Field of view = 2mm)	Plagioclase altered by saussurite. PPL image, 10x (Field of view = 2mm)
Plagioclase altered by saussurite. XPL image, 10x (Field of view = 2mm)