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)

Fibrolite (sillimanite) - Al₂SiO₅

Sillimanite was named by George Thomas Bowen in 1824 in honor of Benjamin Silliman (Professor of Chemistry and Geology, Yale University, New Haven, Connecticut, USA). The minerals kyanite, adalusite and sillimanite are polymorphs of Al₂SiO₅, each occurring under different temperature-pressure regimes and are therefore rarely found together in the same rock. All three polymorphs can be used as index minerals in metamorphic rocks. They all develop in alumina-rich pelites under different conditions of temperature and pressure.

A common variety of sillimanite is known as fibrolite, so named because the mineral appears like a bunch of fibres twisted together when viewed in thin section or even by the naked eye. Both the fibrous and traditional forms of sillimanite are common in metamorphosed sedimentary rocks. It is an index mineral indicating high temperature but variable pressure.

Optical properties:

• Form: Fibrous crystals.
• Color: Colourless.
• Relief: high.
• Cleavage: (010) perfect: thus a basal section of sillimanite, wichh is diamond shaped, has cleavage parallel to the long axis.
• Interference colors: Low (pale yallow).

Al₂SiO₅ phase diagram

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

Fibrous aggregate of sillimanite (fibrolite) in association wtih biotite and quartz. PPL image, 10x (Field of view = 2mm)	Fibrous aggregate of sillimanite (fibrolite) in association wtih biotite and quartz. XPL image, 10x (Field of view = 2mm)	Fibrous aggregate of sillimanite (fibrolite) in association wtih biotite and quartz. PPL image, 10x (Field of view = 2mm)
Fibrous aggregate of sillimanite (fibrolite) in association wtih biotite and quartz. XPL image, 10x (Field of view = 2mm)	Fibrous crystals of sillimanite (fibrolite) enclosed in quartz. PPL image, 10x (Field of view = 2mm)	Fibrous crystals of sillimanite (fibrolite) enclosed in quartz. XPL image, 10x (Field of view = 2mm)
Fibrous crystals of sillimanite (fibrolite) enclosed in quartz. PPL image, 10x (Field of view = 2mm)	Fibrous crystals of sillimanite (fibrolite) enclosed in quartz. XPL image, 10x (Field of view = 2mm)	Fibrous crystals of sillimanite (fibrolite) enclosed in quartz. PPL image, 10x (Field of view = 2mm)
Fibrous crystals of sillimanite (fibrolite) enclosed in quartz. XPL image, 10x (Field of view = 2mm)	Fibrous crystals of sillimanite (fibrolite) enclosed in quartz. PPL image, 20x (Field of view = 1mm)	Fibrous crystals of sillimanite (fibrolite) enclosed in quartz. XPL image, 20x (Field of view = 1mm)
Fibrous crystals of sillimanite (fibrolite) enclosed in quartz. PPL image, 20x (Field of view = 1mm)	Fibrous crystals of sillimanite (fibrolite) enclosed in quartz. XPL image, 20x (Field of view = 1mm)	Fibrous crystals of sillimanite (fibrolite) enclosed in quartz. PPL image, 20x (Field of view = 1mm)
Fibrous crystals of sillimanite (fibrolite) enclosed in quartz. XPL image, 20x (Field of view = 1mm)	Fibrous crystals of sillimanite (fibrolite) enclosed in quartz. PPL image, 20x (Field of view = 1mm)	Fibrous crystals of sillimanite (fibrolite) enclosed in quartz. XPL image, 20x (Field of view = 1mm)
Fibrous crystals of sillimanite (fibrolite). Tibet. PPL image, 20x (Field of view = 1mm)	Fibrous crystals of sillimanite (fibrolite). Tibet. PPL image, 20x (Field of view = 1mm)	Fibrous crystals of sillimanite (fibrolite). Tibet. PPL image, 20x (Field of view = 1mm)
Fibrous crystals of sillimanite (fibrolite). Tibet. PPL image, 10x (Field of view = 2mm)	Fibrous crystals of sillimanite (fibrolite). Tibet. XPL image, 10x (Field of view = 2mm)	Fibrous crystals of sillimanite (fibrolite). Tibet. PPL image, 10x (Field of view = 2mm)
Fibrous crystals of sillimanite (fibrolite). Tibet. XPL image, 10x (Field of view = 2mm)	Fibrous crystals of sillimanite (fibrolite). Tibet. PPL image, 10x (Field of view = 2mm)	Fibrous crystals of sillimanite (fibrolite). Tibet. PPL image, 10x (Field of view = 2mm)
Fibrous crystals of sillimanite (fibrolite). Tibet. PPL image, 10x (Field of view = 2mm)	Fibrous crystals of sillimanite (fibrolite). Tibet. PPL image, 10x (Field of view = 2mm)	Fibrous crystals of sillimanite (fibrolite). Tibet. XPL image, 10x (Field of view = 2mm)
Fibrous crystals of sillimanite (fibrolite). Val Passiria, Bergamo, Italy. PPL image, 10x (Field of view = 2mm)	Fibrous crystals of sillimanite (fibrolite). Val Passiria, Bergamo, Italy. XPL image, 10x (Field of view = 2mm)	Fibrous crystals of sillimanite (fibrolite). Val Passiria, Bergamo, Italy. PPL image, 10x (Field of view = 2mm)
Fibrous crystals of sillimanite (fibrolite). Val Passiria, Bergamo, Italy. PPL image, 10x (Field of view = 2mm)	Fibrous crystals of sillimanite (fibrolite). Val Passiria, Bergamo, Italy. XPL image, 10x (Field of view = 2mm)	Fibrous crystals of sillimanite (fibrolite). Val Passiria, Bergamo, Italy. PPL image, 10x (Field of view = 2mm)
Fibrous crystals of sillimanite (fibrolite). Val Passiria, Bergamo, Italy. PPL image, 20x (Field of view = 1mm)	Fibrous crystals of sillimanite (fibrolite). Val Passiria, Bergamo, Italy. XPL image, 20x (Field of view = 1mm)	Fibrous crystals of sillimanite (fibrolite). Val Passiria, Bergamo, Italy. PPL image, 20x (Field of view = 1mm)
Fibrous crystals of sillimanite (fibrolite). Val Passiria, Bergamo, Italy. PPL image, 20x (Field of view = 1mm)	Fibrous crystals of sillimanite (fibrolite). Val Passiria, Bergamo, Italy. XPL image, 20x (Field of view = 1mm)	Fibrous crystals of sillimanite (fibrolite). Val Passiria, Bergamo, Italy. PPL image, 20x (Field of view = 1mm)
Fibrous crystals of sillimanite (fibrolite). Val Passiria, Bergamo, Italy. PPL image, 20x (Field of view = 1mm)	Fibrous crystals of sillimanite (fibrolite). Val Passiria, Bergamo, Italy. XPL image, 20x (Field of view = 1mm)	Fibrous crystals of sillimanite (fibrolite). Val Passiria, Bergamo, Italy. PPL image, 20x (Field of view = 1mm)
Acicular sillimanite (fibrolite) and biotite crystals. MME (Mafic microgranular enclaves) in the S.Andrea granite. Elba Island, Italy. PPL image, 20x (Field of view = 1mm)	Acicular sillimanite (fibrolite), green spinel and biotite crystals. MME (Mafic microgranular enclaves) in the S.Andrea granite. Elba Island, Italy. PPL image, 20x (Field of view = 1mm)	Acicular sillimanite (fibrolite), green spinel (isotropic) and biotite crystals. MME (Mafic microgranular enclaves) in the S.Andrea granite. Elba Island, Italy. XPL image, 20x (Field of view = 1mm)
Acicular sillimanite (fibrolite) and biotite crystals. MME (Mafic microgranular enclaves) in the S.Andrea granite. Elba Island, Italy. PPL image, 20x (Field of view = 1mm)	Acicular sillimanite (fibrolite) and biotite crystals. MME (Mafic microgranular enclaves) in the S.Andrea granite. Elba Island, Italy. PPL image, 20x (Field of view = 1mm)	Acicular sillimanite (fibrolite) and biotite crystals. MME (Mafic microgranular enclaves) in the S.Andrea granite. Elba Island, Italy. PPL image, 20x (Field of view = 1mm)
Acicular sillimanite (fibrolite) and biotite crystals. MME (Mafic microgranular enclaves) in the S.Andrea granite. Elba Island, Italy. PPL image, 20x (Field of view = 1mm)	Acicular sillimanite (fibrolite) and biotite crystals. MME (Mafic microgranular enclaves) in the S.Andrea granite. Elba Island, Italy. PPL image, 20x (Field of view = 1mm)	Acicular sillimanite (fibrolite) and biotite crystals. MME (Mafic microgranular enclaves) in the S.Andrea granite. Elba Island, Italy. PPL image, 20x (Field of view = 1mm)
Acicular sillimanite (fibrolite) and biotite crystals. PPL image, 20x (Field of view = 1mm)	Acicular sillimanite (fibrolite) and biotite crystals. PPL image, 20x (Field of view = 1mm)	Acicular sillimanite (fibrolite) and biotite crystals. PPL image, 20x (Field of view = 1mm)
Acicular sillimanite (fibrolite) and biotite crystals. XPL image, 20x (Field of view = 1mm)	Acicular sillimanite (fibrolite) and biotite crystals. PPL image, 20x (Field of view = 1mm)	Acicular sillimanite (fibrolite) and biotite crystals. PPL image, 20x (Field of view = 1mm)
Acicular sillimanite (fibrolite) crystals enclosed in a white mica crystal. XPL image, 20x (Field of view = 1mm)	Acicular sillimanite (fibrolite) crystals enclosed in a white mica crystal. XPL image, 20x (Field of view = 1mm)	Acicular sillimanite (fibrolite) crystals enclosed in a white mica crystal. XPL image, 20x (Field of view = 1mm)