Saussurite

Saussurite, named after the Swiss explorer Horace Benedict de Saussure, who discovered it on the slopes of Mont Blanc is a mineral aggregate which is formed as a hydrothermal alteration product of plagioclase feldspar (saussuritization).

saussuritization is a process by which calcium-bearing plagioclase feldspar is altered to a characteristic assemblage of minerals called saussurite; the typical assemblage formed includes zoisite, chlorite, amphibole, and carbonates. Residual fluids present during the late stages of magmatic crystallization can react with previously formed plagioclase feldspar to form saussurite; the saussurite will be spread through the plagioclase or located near its outer margin.
Mafic rocks are especially susceptible to saussuritization owing to their high calcium content; the more calcium-rich portions of plagioclase in acidic rocks also are often saussuritized. The process commonly takes place during the low-grade regional metamorphism of gabbros and basalts, both of which contain plagioclase as an essential component.

Bibliography



• E. WM. Heinrich (1956): Microscopic Petrografy. Mcgraw-hill book company,inc
• David Shelley (1983): Igneous and metamorphic rocks under the microscope. Campman & Hall editori.
• Vernon, R. H. & Clarke, G. L. (2008): Principles of Metamorphic Petrology. Cambridge University Press
• Shelley D (1992): Igneous and Metamorphic Rocks under the Microscope: Classification, textures, microstructures and mineral preferred orientation
• Cox et al. (1979): The Interpretation of Igneous Rocks, George Allen and Unwin, London.

Photo
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Plagioclase altered by Epidote. PPL image, 2x (Field of view = 7mm)
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Plagioclase altered by Epidote. XPL image, 2x (Field of view = 7mm)
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Plagioclase altered by Epidote. PPL image, 10x (Field of view = 2mm)
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Plagioclase altered by Epidote. XPL image, 10x (Field of view = 2mm)
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Plagioclase altered by Epidote. PPL image, 10x (Field of view = 2mm)
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Plagioclase altered by Epidote. XPL image, 10x (Field of view = 2mm)
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Plagioclase altered by Epidote. PPL image, 10x (Field of view = 2mm)
saussuritizzazione(9).jpg

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