Dumortierite- (Al, Fe³⁺)₇O₃(BO₃₎(SiO₄)₃

Dumortierite is a fibrous aluminium boro-silicate mineral, it crystallizes in the orthorhombic system and typically forming fibrous aggregates of slender prismatic crystals. Dumortierite was first described in 1881 for an occurrence in Chaponost, in the Rhöne-Alps of France and named for the French paleontologist Eugène Dumortier (1803–1873). It typically occurs in high temperature aluminium rich regional metamorphic rocks, those resulting from contact metamorphism and also in boron rich pegmatites.

Optical properties:

• Form: Rarely euhedral, usually as small fibrous or columnar aggragate
• Color: Colourless ore pale violet, blue-green or brown
• Relief: High
• Cleavage: (100) good
• Interference colors: Low with first-order colors

dumortierite2020(2).jpg

Radial aggregate of purple acicular crystals of dumortierite. Dehesa, San Diego County, California, USA. From RRUFF.

Blue crystals of dumortierite. Beraketa Commune, Bekily District, Androy Region, Tuléar Province (Toliara), Madagascar. From Wikipedia.

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
Small fibrous (beige color) dumortierite crystals in a dumortierite bearing quartzite. PPL image, 10x (Field of view = 2mm)	Small fibrous (beige color) dumortierite crystals in a dumortierite bearing quartzite. PPL image, 10x (Field of view = 2mm)	Small fibrous (yellow interference colors) dumortierite crystals in a dumortierite bearing quartzite. XPL image, 10x (Field of view = 2mm)
Small fibrous (yellow interference colors) dumortierite crystals in a dumortierite bearing quartzite. XPL image, 10x (Field of view = 2mm)	Small fibrous (beige color) dumortierite crystals in a dumortierite bearing quartzite. PPL image, 10x (Field of view = 2mm)	Small fibrous (yellow interference colors) dumortierite crystals in a dumortierite bearing quartzite. XPL image, 10x (Field of view = 2mm)
Small fibrous (yellow interference colors) dumortierite crystals in a dumortierite bearing quartzite. XPL image, 10x (Field of view = 2mm)	Small fibrous (yellow interference colors) dumortierite crystals in a dumortierite bearing quartzite. XPL image, 10x (Field of view = 2mm)	Small fibrous (beige color) dumortierite crystals in a dumortierite bearing quartzite. PPL image, 2x (Field of view = 7mm)
Small fibrous (yellow interference colors) dumortierite crystals in a dumortierite bearing quartzite. XPL image, 2x (Field of view = 7mm)	Small fibrous (yellow interference colors) dumortierite crystals in a dumortierite bearing quartzite. XPL image, 10x (Field of view = 2mm)	Small fibrous (yellow interference colors) dumortierite crystals in a dumortierite bearing quartzite. XPL image, 10x (Field of view = 2mm)
Small fibrous (yellow interference colors) dumortierite crystals in a dumortierite bearing quartzite. XPL image, 2x (Field of view = 7mm)	Small fibrous (beige color) dumortierite crystals in a dumortierite bearing quartzite. PPL image, 10x (Field of view = 2mm)	Small fibrous (yellow interference colors) dumortierite crystals in a dumortierite bearing quartzite. XPL image, 10x (Field of view = 2mm)
Small fibrous (beige color) dumortierite crystals in a dumortierite bearing quartzite. PPL image, 2x (Field of view = 7mm)	Small fibrous (yellow interference colors) dumortierite crystals in a dumortierite bearing quartzite. XPL image, 10x (Field of view = 2mm)	Small fibrous (yellow interference colors) dumortierite crystals in a dumortierite bearing quartzite. XPL image, 10x (Field of view = 2mm)
Small fibrous (from colorless to pale blu-liliac) dumortierite crystals in a dumortierite bearing quartzite. PPL image, 10x (Field of view = 2mm)	Small fibrous dumortierite crystals in a dumortierite bearing quartzite. XPL image, 10x (Field of view = 2mm)	Small fibrous (from colorless to pale blu-liliac) dumortierite crystals in a dumortierite bearing quartzite. PPL image, 10x (Field of view = 2mm)
Small fibrous (from colorless to pale blu-liliac) dumortierite crystals in a dumortierite bearing quartzite. PPL image, 10x (Field of view = 2mm)	Small fibrous dumortierite crystals in a dumortierite bearing quartzite. XPL image, 10x (Field of view = 2mm)	Small fibrous (from colorless to pale blu-liliac) dumortierite crystals in a dumortierite bearing quartzite. PPL image, 10x (Field of view = 2mm)
Small fibrous (from colorless to pale blu-liliac) dumortierite crystals in a dumortierite bearing quartzite. PPL image, 10x (Field of view = 2mm)	Small fibrous (from colorless to pale blu-liliac) dumortierite crystals in a dumortierite bearing quartzite. PPL image, 10x (Field of view = 2mm)	Small fibrous dumortierite crystals in a dumortierite bearing quartzite. XPL image, 10x (Field of view = 2mm)
Small fibrous (from colorless to pale blu-liliac) dumortierite crystals in a dumortierite bearing quartzite. PPL image, 10x (Field of view = 2mm)	Small fibrous (from colorless to pale blu-liliac) dumortierite crystals in a dumortierite bearing quartzite. PPL image, 10x (Field of view = 2mm)	Small fibrous (from colorless to pale blu-liliac) dumortierite crystals in a dumortierite bearing quartzite. PPL image, 10x (Field of view = 2mm)
Small fibrous (from colorless to pale blu-liliac) dumortierite crystals in a dumortierite bearing quartzite. PPL image, 10x (Field of view = 2mm)	Small fibrous dumortierite crystals in a dumortierite bearing quartzite. XPL image, 10x (Field of view = 2mm)	Small fibrous (from colorless to pale blu-liliac) dumortierite crystals in a dumortierite bearing quartzite. PPL image, 10x (Field of view = 2mm)
Small fibrous (from colorless to pale blu-liliac) dumortierite crystals in a dumortierite bearing quartzite. PPL image, 20x (Field of view = 1mm)	Small fibrous (from colorless to pale blu-liliac) dumortierite crystals in a dumortierite bearing quartzite. PPL image, 20x (Field of view = 1mm)	Small fibrous (from colorless to pale blu-liliac) dumortierite crystals in a dumortierite bearing quartzite. PPL image, 20x (Field of view = 1mm)

Metamorphic Minerals

Texture and Microstructure

Metamorphic Rocks

Dumortierite- (Al, Fe3+)7O3(BO3)(SiO4)3

Dumortierite- (Al, Fe³⁺)₇O₃(BO₃₎(SiO₄)₃