Eutaxitic Texture

Eutaxitic texture describes the layered or banded texture in explosive volcanic rocks. It is often caused by the compaction and flattening of glass shards and pumice fragments. Ignimbrites are typically characterized by fist-sized pumice fragments floating in a finer grained matrix but many ignimbrites, however, are still hot when they are emplaced so that the pumice and ash fragments are still plastic and malleable. Thick, hot ignimbrites will often collapse under their own weight, thus fusing the fragments together to generate a welded flow. In such cases the pumice fragments are compacted into dark, glassy pancake shapes, called fiamme. A welded ignimbrite containing fiamme is said to have a eutaxitic texture.

ignimbrites(1).jpg

Ignimbrite sample from the Southern coast of Gran Canaria. Note the strongly flattened pumice fragments (fiamme). From Sand Atlas.

Ignimbrite sample from the Western part of Gran Canaria. From Sand Atlas.

Ignimbrite sample from the NE coast of Gran Canaria. From Sand Atlas.

Bibliography

• Cox et al. (1979): The Interpretation of Igneous Rocks, George Allen and Unwin, London.
• Howie, R. A., Zussman, J., & Deer, W. (1992). An introduction to the rock-forming minerals (p. 696). Longman.
• Le Maitre, R. W., Streckeisen, A., Zanettin, B., Le Bas, M. J., Bonin, B., Bateman, P., & Lameyre, J. (2002). Igneous rocks. A classification and glossary of terms, 2. Cambridge University Press.
• Middlemost, E. A. (1986). Magmas and magmatic rocks: an introduction to igneous petrology.
• 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.

Photo
Rheomorphic structures (flow structures) in a ignimbrite from vulsini (Italy). PPL image , 10x (Field of view = 2mm)	Rheomorphic structures (flow structures) in a ignimbrite from vulsini (Italy). PPL image , 10x (Field of view = 2mm)	Rheomorphic structures (flow structures) in a ignimbrite from vulsini (Italy). PPL image , 10x (Field of view = 2mm)
Rheomorphic structures (flow structures) in a ignimbrite from vulsini (Italy). PPL image , 10x (Field of view = 2mm)	Rheomorphic structures (flow structures) in a ignimbrite from vulsini (Italy). PPL image , 10x (Field of view = 2mm)	Rheomorphic structures (flow structures) in a ignimbrite from vulsini (Italy). PPL image , 10x (Field of view = 2mm)
Rheomorphic structures (flow structures) in a ignimbrite from vulsini (Italy). PPL image , 10x (Field of view = 2mm)	Rheomorphic structures (flow structures) in a ignimbrite from vulsini (Italy). PPL image , 10x (Field of view = 2mm)	Rheomorphic structures (flow structures) in a ignimbrite from vulsini (Italy). PPL image , 10x (Field of view = 2mm)
Rheomorphic structures (flow structures) in a ignimbrite from vulsini (Italy). PPL image , 10x (Field of view = 2mm)	Rheomorphic structures (flow structures) in a ignimbrite from vulsini (Italy). PPL image , 10x (Field of view = 2mm)	Rheomorphic structures (flow structures) in a ignimbrite from vulsini (Italy). PPL image , 10x (Field of view = 2mm)
Rheomorphic structures (flow structures) in a ignimbrite from vulsini (Italy). PPL image , 10x (Field of view = 2mm)	Rheomorphic structures (flow structures) in a ignimbrite from vulsini (Italy). PPL image , 10x (Field of view = 2mm)	Rheomorphic structures (flow structures) in a ignimbrite from vulsini (Italy). PPL image , 10x (Field of view = 2mm)
Rheomorphic structures (flow structures) in a ignimbrite from vulsini (Italy). PPL image , 10x (Field of view = 2mm)	Rheomorphic structures (flow structures) in a ignimbrite from vulsini (Italy). PPL image , 10x (Field of view = 2mm)	< Rheomorphic structures (flow structures) in a ignimbrite from vulsini (Italy). PPL image , 10x (Field of view = 2mm)
Rheomorphic structures (flow structures) in a ignimbrite from vulsini (Italy). PPL image , 10x (Field of view = 2mm)	Rheomorphic structures (flow structures) in a ignimbrite from vulsini (Italy). PPL image , 10x (Field of view = 2mm)	Rheomorphic structures (flow structures) in a ignimbrite from vulsini (Italy). PPL image , 10x (Field of view = 2mm)