Metamorphic Minerals

Texture and Microstructure

Metamorphic Rocks

Chloritoid (ottrelite) - (Fe²⁺,Mg,Mn)₂Al₄Si₂O₁₀(OH)₄

Chloritoid, Named in 1837 by Gustav Rose for the visual similarity to chlorite-group minerals, is a silicate mineral of metamorphic origin. It was first described from localities in the Ural Mountains region of Russia. Manganese-rich chloritoid is known as ottrelite; the magnesium-rich variety is called sismondine.

It occurs as greenish grey to black platy micaceous crystals and foliated masses. It typically occurs in phyllites, schists and marbles. Chloritoid Results from low to medium grade regional metamorphism as well as in hydrothermal environments. Common associative minerals are muscovite, chlorite, garnet, staurolite and kyanite.

Optical properties:
• Form: Closely resembles mica minerals, occurring as pseudo-hexagonal tabular crystals.
• Color: Colourless, green, blue green.
• Relief: High.
• Cleavage: (001) perfect.
• Interference colors: Low but masked by the greenish color of the mineral: anomalous blue colors are often seen.

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.

Chloritoid crystals (the rectangular gree-blue crystals) in a impure marble from Orbetello, Italy. PPL image, 2x (Field of view = 7mm)	Chloritoid crystals in a impure marble from Orbetello, Italy. PPL image, 2x (Field of view = 7mm)	Chloritoid crystals (the rectangular gree-blue crystals) in a impure marble from Orbetello, Italy. PPL image, 2x (Field of view = 7mm)
Chloritoid crystals (the rectangular gree-blue crystals) in a impure marble from Orbetello, Italy. PPL image, 2x (Field of view = 7mm)	Chloritoid crystal with Hour-Glass Zoning in a impure marble from Orbetello, Italy. PPL image, 10x (Field of view = 2mm)	Chloritoid crystals (the rectangular gree-blue crystals) in a impure marble from Orbetello, Italy. PPL image, 2x (Field of view = 7mm)
Chloritoid crystals (the rectangular gree-blue crystals) in a impure marble from Orbetello, Italy. PPL image, 2x (Field of view = 7mm)	Chloritoid crystals in a impure marble from Orbetello, Italy. XPL image, 2x (Field of view = 7mm)	Chloritoid crystals (the rectangular gree-blue crystals) in a impure marble from Orbetello, Italy. PPL image, 2x (Field of view = 7mm)
Chloritoid crystals in a impure marble from Orbetello, Italy. PPL image, 10x (Field of view = 2mm)	Chloritoid crystals in a impure marble from Orbetello, Italy. PPL image, 10x (Field of view = 2mm)	Chloritoid crystals in a impure marble from Orbetello, Italy. PPL image, 10x (Field of view = 2mm)
Chloritoid crystals (the rectangular gree-blue crystals) in a impure marble from Orbetello, Italy. PPL image, 2x (Field of view = 7mm)	Chloritoid crystals in a impure marble from Orbetello, Italy. XPL image, 2x (Field of view = 7mm)	Chloritoid crystals in a impure marble from Orbetello, Italy. XPL image, 2x (Field of view = 7mm)
Chloritoid (ottrelite) porphyroblasts in a fine-grained slate. Otterly, Ardennes (Belgium). PPL image, 2x (Field of view = 7mm)	Chloritoid (ottrelite) porphyroblasts in a fine-grained slate. Otterly, Ardennes (Belgium). PPL image, 2x (Field of view = 7mm)	Chloritoid (ottrelite) porphyroblasts in a fine-grained slate. Otterly, Ardennes (Belgium). PPL image, 2x (Field of view = 7mm)
Chloritoid (ottrelite) porphyroblasts in a fine-grained slate. Otterly, Ardennes (Belgium). PPL image, 2x (Field of view = 7mm)	Chloritoid (ottrelite) porphyroblasts in a fine-grained slate. Otterly, Ardennes (Belgium). PPL image, 2x (Field of view = 7mm)	Chloritoid (ottrelite) porphyroblasts in a fine-grained slate. Otterly, Ardennes (Belgium). XPL image, 2x (Field of view = 7mm)
Chloritoid (ottrelite) porphyroblasts in a fine-grained slate. Otterly, Ardennes (Belgium). PPL image, 2x (Field of view = 7mm)	Chloritoid (ottrelite) porphyroblasts in a fine-grained slate. Otterly, Ardennes (Belgium). PPL image, 2x (Field of view = 7mm)	Chloritoid (ottrelite) porphyroblasts in a fine-grained slate. Otterly, Ardennes (Belgium). XPL image, 2x (Field of view = 7mm)
Chloritoid (ottrelite) porphyroblasts in a fine-grained slate. Otterly, Ardennes (Belgium). PPL image, 2x (Field of view = 7mm)	Chloritoid (ottrelite) porphyroblasts in a fine-grained slate. Otterly, Ardennes (Belgium). XPL image, 2x (Field of view = 7mm)	Chloritoid (ottrelite) porphyroblasts in a fine-grained slate. Otterly, Ardennes (Belgium). PPL image, 2x (Field of view = 7mm)
Chloritoid (ottrelite) porphyroblasts in a fine-grained slate. Otterly, Ardennes (Belgium). PPL image, 2x (Field of view = 7mm)	Chloritoid (ottrelite) porphyroblast (with Hour-Glass inclusions) in a fine-grained slate. Otterly, Ardennes (Belgium). PPL image, 10x (Field of view = 2mm)	Chloritoid (ottrelite) porphyroblast (with Hour-Glass inclusions) in a fine-grained slate. Otterly, Ardennes (Belgium). PPL image, 10x (Field of view = 2mm)
Radiating aggregates of chloritoid crystals. PPL image, 10x (Field of view = 2mm)	Radiating aggregates of chloritoid crystals. XPL image, 10x (Field of view = 2mm)	Radiating aggregates of chloritoid crystals. PPL image, 10x (Field of view = 2mm)
Radiating aggregates of chloritoid crystals. XPL image, 10x (Field of view = 2mm)	Chloritoid crystals in a schist. PPL image, 2x (Field of view = 7mm)	Chloritoid crystals in a schist. PPL image, 2x (Field of view = 7mm)
Chloritoid crystal (with Hour-Glass inclusions) in a schist. PPL image, 10x (Field of view = 2mm)	Chloritoid crystal (with Hour-Glass inclusions) in a schist. PPL image, 10x (Field of view = 2mm)	Chloritoid crystals in a schist. XPL image, 2x (Field of view = 7mm)
Chloritoid crystals in a schist. XPL image, 2x (Field of view = 7mm)	Chloritoid crystal in a schist. PPL image, 10x (Field of view = 2mm)	Chloritoid crystal in a schist. XPL image, 10x (Field of view = 2mm)
Radiating aggregates of chloritoid crystals in a metasandstone. PPL image, 10x (Field of view = 2mm)	Radiating aggregates of chloritoid crystals in a metasandstone. XPL image, 10x (Field of view = 2mm)	Radiating aggregates of chloritoid crystals in a metasandstone. PPL image, 2x (Field of view = 7mm)
Radiating aggregates of chloritoid crystals in a metasandstone. PPL image, 2x (Field of view = 7mm)	Radiating aggregates of chloritoid crystals in a metasandstone. XPL image, 2x (Field of view = 7mm)	Radiating aggregates of chloritoid crystals in a metasandstone. PPL image, 2x (Field of view = 7mm)
Radiating aggregates of chloritoid crystals in a metasandstone. PPL image, 2x (Field of view = 7mm)	Radiating aggregates of chloritoid crystals in a metasandstone. PPL image, 10x (Field of view = 2mm)	Radiating aggregates of chloritoid crystals in a metasandstone. XPL image, 10x (Field of view = 2mm)
Radiating aggregates of chloritoid crystals in a metasandstone. PPL image, 10x (Field of view = 2mm)	Radiating aggregates of chloritoid crystals in a metasandstone. XPL image, 10x (Field of view = 2mm)	Radiating aggregates of chloritoid crystals in a metasandstone. XPL image, 10x (Field of view = 2mm)
Radiating aggregates of chloritoid crystals in a metasandstone. XPL image, 10x (Field of view = 2mm)	Radiating aggregates of chloritoid crystals in a metasandstone. XPL image, 10x (Field of view = 2mm)	Radiating aggregates of chloritoid crystals in a metasandstone. XPL image, 10x (Field of view = 2mm)
chloritoid crystals in a deformed Mica-Schist. PPL image, 2x (Field of view = 7mm)	chloritoid crystals in a deformed Mica-Schist. PPL image, 2x (Field of view = 7mm)	chloritoid crystals in a deformed Mica-Schist. PPL image, 2x (Field of view = 7mm)
chloritoid crystals in a deformed Mica-Schist. PPL image, 2x (Field of view = 7mm)	chloritoid crystals in a deformed Mica-Schist. PPL image, 2x (Field of view = 7mm)	chloritoid crystals in a deformed Mica-Schist. XPL image, 2x (Field of view = 7mm)
chloritoid crystals in a deformed Mica-Schist. XPL image, 2x (Field of view = 7mm)	chloritoid crystals in a deformed Mica-Schist. PPL image, 10x (Field of view = 2mm)	chloritoid crystals in a deformed Mica-Schist. PPL image, 10x (Field of view = 2mm)
Chloritoid (green) crystals in a schist. Monte Altissimo, Apuane Alps, Tuscany, Italy. PPL image, 2x (Field of view = 7mm)	Chloritoid crystals in a schist. Monte Altissimo, Apuane Alps, Tuscany, Italy. XPL image, 2x (Field of view = 7mm)	Chloritoid (green) crystals in a schist. Monte Altissimo, Apuane Alps, Tuscany, Italy. PPL image, 2x (Field of view = 7mm)
Chloritoid crystals in a schist. Monte Altissimo, Apuane Alps, Tuscany, Italy. XPL image, 2x (Field of view = 7mm)	Chloritoid (green) and calcite crystals in a schist. Monte Altissimo, Apuane Alps, Tuscany, Italy. PPL image, 10x (Field of view = 2mm)	Chloritoid and calcite crystals in a schist. Monte Altissimo, Apuane Alps, Tuscany, Italy. XPL image, 10x (Field of view = 2mm)
Chloritoid (green) and calcite crystals in a schist. Monte Altissimo, Apuane Alps, Tuscany, Italy. PPL image, 10x (Field of view = 2mm)	Chloritoid and calcite crystals in a schist. Monte Altissimo, Apuane Alps, Tuscany, Italy. XPL image, 10x (Field of view = 2mm)	Chloritoid (green) crystals in a schist. Monte Altissimo, Apuane Alps, Tuscany, Italy. PPL image, 2x (Field of view = 7mm)
Chloritoid crystals in a schist. Monte Altissimo, Apuane Alps, Tuscany, Italy. XPL image, 2x (Field of view = 7mm)	Chloritoid (green) crystals in a schist. Monte Altissimo, Apuane Alps, Tuscany, Italy. PPL image, 2x (Field of view = 7mm)	Chloritoid crystals in a schist. Monte Altissimo, Apuane Alps, Tuscany, Italy. XPL image, 2x (Field of view = 7mm)
Chloritoid crystals in a schist. Monte Altissimo, Apuane Alps, Tuscany, Italy. XPL image, 10x (Field of view = 2mm)	Chloritoid (green) crystals in a schist. Monte Altissimo, Apuane Alps, Tuscany, Italy. PPL image, 10x (Field of view = 2mm)	Chloritoid (green) crystals in a schist. Monte Altissimo, Apuane Alps, Tuscany, Italy. PPL image, 10x (Field of view = 2mm)
Chloritoid (green) crystal in a schist. Monte Altissimo, Apuane Alps, Tuscany, Italy. PPL image, 10x (Field of view = 2mm)	Chloritoid crystal in a schist. Monte Altissimo, Apuane Alps, Tuscany, Italy. XPL image, 10x (Field of view = 2mm)	Chloritoid (green) crystals in a schist. Monte Altissimo, Apuane Alps, Tuscany, Italy. PPL image, 10x (Field of view = 2mm)
Cristallo di cloritoide (verde) in uno scisto. Monte Altissimo, Alpi Apuane, Toscana. Immagine a N//, 10x (lato lungo = 2mm)	Chloritoid crystal in a schist. Monte Altissimo, Apuane Alps, Tuscany, Italy. XPL image, 10x (Field of view = 2mm)	Chloritoid (green) crystals in a schist. Monte Altissimo, Apuane Alps, Tuscany, Italy. PPL image, 10x (Field of view = 2mm)
Chloritoid (green) crystal in a schist. Monte Altissimo, Apuane Alps, Tuscany, Italy. PPL image, 10x (Field of view = 2mm)	Chloritoid crystal in a schist. Monte Altissimo, Apuane Alps, Tuscany, Italy. XPL image, 10x (Field of view = 2mm)	Chloritoid (green) crystals in a schist. Monte Altissimo, Apuane Alps, Tuscany, Italy. PPL image, 10x (Field of view = 2mm)

Metamorphic Minerals

Texture and Microstructure

Metamorphic Rocks

Chloritoid (ottrelite) - (Fe2+,Mg,Mn)2Al4Si2O10(OH)4

Chloritoid (ottrelite) - (Fe²⁺,Mg,Mn)₂Al₄Si₂O₁₀(OH)₄