Ribbon

Ribbons are highly elongated disc- or lens-shaped crystal or aggregate of quartz, common in mylonites and high-grade rocks. In thin section the crystals are ribbon-shaped, hence the name. Quartz ribbons form by flattening of originally equidimensional quartz grains, or possibly by migration of grain boundaries to form single large grains from more fine-grained parent aggregates. They may exhibit undulose extinction, or be recrystallised into polycrystalline ribbons

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
Quartz ribbons in a mylonite. XPL image, 2x (Field of view = 7mm)	Quartz ribbons in a mylonite. XPL image, 2x (Field of view = 7mm)	Quartz ribbons in a mylonite. XPL image, 2x (Field of view = 7mm)
Deformation lamellae in a quartz ribbons in a mylonite. XPL image, 10x (Field of view = 2mm)	Deformation lamellae in a quartz ribbons in a mylonite. XPL image, 10x (Field of view = 2mm)	Quartz ribbons in a mylonite. XPL image, 10x (Field of view = 2mm)
Quartz ribbons in a mylonite. XPL image, 2x (Field of view = 7mm)	Quartz ribbons in a mylonite. XPL image, 2x (Field of view = 7mm)	Quartz ribbons in a mylonite. XPL image, 10x (Field of view = 2mm)
Quartz ribbons in a mylonite. XPL image, 10x (Field of view = 2mm)	Quartz ribbons in a mylonite. XPL image, 10x (Field of view = 2mm)	Quartz ribbons, around garnet, in a mylonite. PPL image, 2x (Field of view = 7mm)
Quartz ribbons, around garnet, in a mylonite. XPL image, 2x (Field of view = 7mm)	Quartz ribbons in a mylonite. XPL image, 2x (Field of view = 7mm)	Quartz ribbons, around garnet, in a mylonite. PPL image, 2x (Field of view = 7mm)
Quartz ribbons, around garnet, in a mylonite. PPL image, 2x (Field of view = 7mm)	Quartz ribbons in a mylonite. PPL image, 2x (Field of view = 7mm)	Quartz ribbons in a mylonite. PPL image, 2x (Field of view = 7mm)