Piemontite - Ca2(Mn,Fe)Al2(SiO4)(Si2O7)O(OH)

Named in 1853 by Gustav Adolph Kenngott for the type locality, the Piemonte region of Italy. Piemontite probably forms complete solid solution with all compositions of the clinozoisite-epidote series and differs from it by the presence of Manganese. Less than 1% of Mn2O3 is sufficient to produce the pink-red colors and strong pleochroism that are probably the best defining characteristics of Piemontite. The most common occurrence of piemontite is in schists of low-medium grade regional metamorphism in association with chlorite, quartz and sericite. Piemontite may appear in Manganese deposits of metasomatic or hydrothermal origin.

Optical properties:

Form: Columnar, bladed or acicular crystals.
Color: Pink, red
Pleochroism: Strong, from red-pink to yellow.
Relief: High
Cleavage: Perfect basal cleavage (001).
Interference colors: Mild to strong birefringence. Often masked by intense mineral color.


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Elongated piemontite purple crystals associated with albite. Praborna mine, Aosta Valley, St. Marcel, Italy. From RRUFF.




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Elongated piemontite purple crystals associated with albite. Muramatsu mine, Kinkai, Nagasaki, Japan. From RRUFF.




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Elongated piemontite purple crystals associated with albite. Muramatsu mine, Kinkai, Nagasaki, Japan. From RRUFF.




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
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Pink Piemontite crystals from Apuan Alps, Italy. PPL image, 2x (Field of view = 7mm)
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Piemontite crystals from Apuan Alps, Italy. XPL image, 2x (Field of view = 7mm)
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Pink-yellow Piemontite crystals from Apuan Alps, Italy. PPL image, 2x (Field of view = 7mm)
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Pink-yellow Piemontite crystals from Apuan Alps, Italy. PPL image, 2x (Field of view = 7mm)
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Pink-yellow Piemontite crystals from Apuan Alps, Italy. PPL image, 2x (Field of view = 7mm)
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Pink-yellow Piemontite crystals from Apuan Alps, Italy. PPL image, 2x (Field of view = 7mm)
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Pink-yellow Piemontite crystals from Apuan Alps, Italy. PPL image, 2x (Field of view = 7mm)
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Piemontite crystals from Apuan Alps, Italy. XPL image, 2x (Field of view = 7mm)
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Pink-yellow Piemontite crystals from Apuan Alps, Italy. PPL image, 10x (Field of view = 2mm)
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Pink-yellow Piemontite crystals from Apuan Alps, Italy. PPL image, 2x (Field of view = 7mm)
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Pink-yellow Piemontite crystals from Apuan Alps, Italy. PPL image, 2x (Field of view = 7mm)
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Pink-yellow Piemontite crystals from Apuan Alps, Italy. PPL image, 2x (Field of view = 7mm)
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Pink-yellow Piemontite crystals from Apuan Alps, Italy. PPL image, 10x (Field of view = 2mm)
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Piemontite crystals from Apuan Alps, Italy. XPL image, 10x (Field of view = 2mm)
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Pink-yellow Piemontite crystals from Apuan Alps, Italy. PPL image, 10x (Field of view = 2mm)
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Pink-yellow Piemontite crystals from Apuan Alps, Italy. PPL image, 10x (Field of view = 2mm)
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Pink-yellow Piemontite crystals from Apuan Alps, Italy. PPL image, 10x (Field of view = 2mm)
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Pink-yellow Piemontite crystals from Apuan Alps, Italy. PPL image, 10x (Field of view = 2mm)
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Pink Piemontite crystals from Apuan Alps, Italy. PPL image, 10x (Field of view = 2mm)
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Pink Piemontite crystals from Apuan Alps, Italy. PPL image, 2x (Field of view = 7mm)
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Pink Piemontite crystals from Apuan Alps, Italy. PPL image, 2x (Field of view = 7mm)
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Pink Piemontite crystals from Apuan Alps, Italy. PPL image, 10x (Field of view = 2mm)
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Pink Piemontite crystals from Apuan Alps, Italy. PPL image, 10x (Field of view = 2mm)
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Piemontite crystals from Apuan Alps, Italy. XPL image, 10x (Field of view = 2mm)
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Piemontite crystals from Apuan Alps, Italy. PPL image, 2x (Field of view = 7mm)
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Piemontite crystals from Apuan Alps, Italy. PPL image, 2x (Field of view = 7mm)
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Piemontite crystals from Apuan Alps, Italy. PPL image, 2x (Field of view = 7mm)
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Piemontite crystals from Apuan Alps, Italy. PPL image, 2x (Field of view = 7mm)
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Piemontite crystals from Apuan Alps, Italy. PPL image, 2x (Field of view = 7mm)
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Piemontite crystals from Apuan Alps, Italy. PPL image, 10x (Field of view = 2mm)
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Piemontite crystals from Apuan Alps, Italy. PPL image, 10x (Field of view = 2mm)
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Piemontite crystals from Apuan Alps, Italy. PPL image, 10x (Field of view = 2mm)
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Piemontite crystals from Apuan Alps, Italy. PPL image, 10x (Field of view = 2mm)
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Piemontite crystals in a schist from Apuan Alps, Italy. PPL image, 2x (Field of view = 7mm)
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Piemontite crystals in a schist from Apuan Alps, Italy. PPL image, 2x (Field of view = 7mm)
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Piemontite crystals in a schist from Apuan Alps, Italy. PPL image, 2x (Field of view = 7mm)
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Piemontite crystals in a schist from Apuan Alps, Italy. PPL image, 2x (Field of view = 7mm)
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Piemontite crystals in a schist from Apuan Alps, Italy. PPL image, 2x (Field of view = 7mm)
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Piemontite crystals in a schist from Apuan Alps, Italy. PPL image, 2x (Field of view = 7mm)
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Piemontite rich layers alternating with quartz-garnet rich layers. Mn-Metachert. PPL image, 1x (Field of view = 9mm)
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Piemontite rich layers alternating with quartz-garnet rich layers. Mn-Metachert. PPL image, 1x (Field of view = 9mm)
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Piemontite rich layers alternating with quartz-garnet rich layers. Mn-Metachert. XPL image, 1x (Field of view = 9mm)
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Piemontite rich layers alternating with quartz-garnet rich layers. Mn-Metachert. PPL image, 1x (Field of view = 9mm)
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Piemontite rich layers alternating with quartz-garnet rich layers. Mn-Metachert. PPL image, 1x (Field of view = 9mm)
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Piemontite rich layers alternating with quartz-garnet rich layers. Mn-Metachert. XPL image, 1x (Field of view = 9mm)
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Piemontite rich layers alternating with quartz-garnet rich layers. Mn-Metachert. PPL image, 2x (Field of view = 7mm)
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Piemontite rich layers alternating with quartz-garnet rich layers. Mn-Metachert. PPL image, 2x (Field of view = 7mm)
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Piemontite rich layers alternating with quartz-garnet rich layers. Mn-Metachert. PPL image, 2x (Field of view = 7mm)
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Piemontite rich layers alternating with quartz-garnet rich layers. Mn-Metachert. PPL image, 2x (Field of view = 7mm)
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Piemontite rich layers alternating with quartz-garnet rich layers. Mn-Metachert. PPL image, 2x (Field of view = 7mm)
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Piemontite rich layers alternating with quartz-garnet rich layers. Mn-Metachert. XPL image, 2x (Field of view = 7mm)
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Piemontite rich layers alternating with quartz-garnet rich layers. Mn-Metachert. PPL image, 2x (Field of view = 7mm)
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Piemontite and garnet crystals. Mn-Metachert. PPL image, 2x (Field of view = 7mm)
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Piemontite crystals. Mn-Metachert. PPL image, 10x (Field of view = 2mm)
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Piemontite rich layers alternating with quartz-garnet rich layers. Mn-Metachert. PPL image, 10x (Field of view = 2mm)
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Piemontite rich layers alternating with quartz-garnet rich layers. Mn-Metachert. XPL image, 10x (Field of view = 2mm)
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Piemontite rich layers alternating with quartz-garnet rich layers. Mn-Metachert. PPL image, 10x (Field of view = 2mm)
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Piemontite crystals. Mn-Metachert. PPL image, 10x (Field of view = 2mm)
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Piemontite and garnet crystals. Mn-Metachert. PPL image, 2x (Field of view = 7mm)
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Piemontite and garnet crystals. Mn-Metachert. PPL image, 2x (Field of view = 7mm)
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Piemontite rich layers alternating with quartz-garnet rich layers. Mn-Metachert. PPL image, 2x (Field of view = 7mm)
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Piemontite rich layers alternating with quartz-garnet rich layers. Mn-Metachert. PPL image, 2x (Field of view = 7mm)
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Piemontite rich layers alternating with quartz-garnet rich layers. Mn-Metachert. PPL image, 2x (Field of view = 7mm)
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Piemontite rich layers alternating with quartz-garnet rich layers. Mn-Metachert. XPL image, 2x (Field of view = 7mm)
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Piemontite rich layers alternating with quartz-garnet rich layers. Mn-Metachert. PPL image, 2x (Field of view = 7mm)
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Piemontite rich layers alternating with quartz-garnet rich layers. Mn-Metachert. PPL image, 2x (Field of view = 7mm)
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Piemontite and garnet crystals. Mn-Metachert. PPL image, 20x (Field of view = 1mm)
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Piemontite and garnet crystals. Mn-Metachert. PPL image, 20x (Field of view = 1mm)
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Piemontite and garnet crystals. Mn-Metachert. PPL image, 10x (Field of view = 2mm)