Metamorphic Minerals

• Actinolite
• Alurgite
• Andalusite
• Andalusite (chiastolite)
• Antigorite
• Anthophyllite-Gedrite
• Biotite
• Brucite
• Calcite
• Cassiterite
• Charoite
• Chlorite
• Chloritoid
• Chrysocolla
• Cordierite
• Corundum
• Corundum (ruby)
• Kyanite
• Kornerupine
• Kyanite (reticite)
• Deerite
• Dumortierite
• Epidotes
Allanite
Pistacite
Piemontite
Zoisite

• Fassaite
• Fluorite
• Glaucophane
• Garnet
• Hercynite
• Hedenbergite
• Hydrogrossular
• Howieite
• Humites
• Jadeite
• Lawsonite
• Lazulite
• Lazurite
• Malachite
• Minnesotaite
• Muscovite
• Olivine
• Omphacite
• Omphacite Cr
• Pargasite
• Piemontite (Praborna)
• Pyrite
• Prehnite
• Pumpellyite
• Quartz
• Rhodonite
• Rutile
• Sapphirine
• Scapolite
• Serpentine
• Sillimanite
• Sillimanite (fibrolite)
• Staurolite
• Stilpnomelane
• Sugilite
• Talc
• Taramellite
• Thulite
• Tinaksite
• Tinzenite
• Titanite
• Tremolite
• Tourmaline
• Vesuvianite
• Violan
• Wollastonite
• Yoderite
• Zussmanite

Texture and Microstructure

• Augen
• Book shelf sliding
• Boudinage
• Corona
• Decussate
• Deformation lamellae
• Deformation twins
• Crenulation cleavage
• Fringes
• Granoblastic
• Kelyphite
• Kink Bands
• Lepidoblastic
• Mesh
• Mica fish
• Mylonitic
• Nematoblastic
• Oblique foliations
• Polygonal
• Porphyroblastic
• Porphyroclastic
• Pseudomorph
• Ribbon
• S-C fabric
• Skeletal garnet
• Symplectite
• Veins

Metamorphic Rocks

• Albite greenshist
• Amphibolite (felsic)
• Amphibolite (mafic)
• Amphibolite (mylonitic)
• Amphibolite with epidote
• Andalusite schist
• Anyolite
• Augen gneiss
• Blueschist
• Blueschist (Ile de Groix)
• Blueschist (retrograde)
• Buchite
• Calc-schists
• Carbonated peridotite
• Cataclasite
• Charoitite
• Chlorite schist
• Chloritoid Schist (Ile de Groix)
• Cordierite slate
• Corundum-fuchsite rock
• Deformed oolite
• Dunite (mylonitic)
• Eclogite
• Eclogite Porto Ottiolu
• Epidosite
• Gabbro (mylonitic)
• Garnet micaschist
• Glaucophane granofels
• Granite (mylonitic)
• Granulite (felsic)
• Granulite (mafic)
• Granulite (retrograde)
• Granulite (sapphirine-bearing)
• Greenschist
• Hornfels
• Hornfels (albite-epidote)
• Hornfels (cordierite, plagioclase)
• Hornfels (corundum, plagioclase)
• Hornfels (hydrogarnet)
• Jadeite metagranite
• Jadeitite
• Kinzigite
• Lapis lazuli
• Marble
• Marble (calc-silicate)
• Marble (diopside)
• Marble (forsterite)
• Marble (mylonitic)
• Marble (tremolite)
• Mylonite
• Ocean jasper
• Ophicalcite
• Peridotite (mylonitic)
• Phyllite
• Prasinite
• Pseudotachylyte
• Pseudotachylyte (Ivrea-Verbano)
• Quartzite
• Quartzite (tourmaline)
• Rhyolite (mylonitic)
• Rodingite
• Schist
• Seafloor basalt
• Serpentinite
• Serpentinized lherzolite
• Skarn
• Skiddaw Metamorphic Aureole
Skiddaw
1) Spotted slate
2) Andalusite slate
3) Cordierite slate

• Slate
• Slate (ottrelite)
• Talc schist
• Tourmalinite
• Ultramylonite (granitic)
• Ultramylonite (mafic)

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.

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

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

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

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