Trachytic Texture

Trachytic is a texture of extrusive rocks in which the groundmass contains little volcanic glass and consists predominantly of minute tabular crystals, namely, sanidine microlites. The microlites are parallel, forming flow lines along the directions of lava flow and around inclusions. Trachytic texture occurs in rocks that are rich in alkalies; hence the vitreous mass of the rocks has a relatively low viscosity. Trachytic texture is especially characteristic of trachytes and rocks similar to trachytes. Trachytic textures are often attributed to flow orientation, however, there is little evidence to support this. Macroscopic trachytic textures visible with the naked eye are sometimes called trachytoid textures.

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Sanidine phenocryst within a trachyte, Drachenfels, Germany. From Nuno Correia.

Sanidine phenocryst within a trachyte, Drachenfels, Germany. From P. Klimetz.

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
Trachytic Texture in a Trachyte from Italy. XPL image, 10x (Field of view = 2mm)	Trachytic Texture in a Trachyte from Italy. XPL image, 10x (Field of view = 2mm)	Trachytic Texture in a Trachyte from Italy. XPL image, 10x (Field of view = 2mm)
Trachytic Texture in a Trachyte from Italy. XPL image, 10x (Field of view = 2mm)	Trachytic Texture in a Trachyte from Italy. XPL image, 10x (Field of view = 2mm)	Trachytic Texture in a Trachyte from Antarctica. The green crystals are Aegirine. PPL image, 2x (Field of view = 7mm)
Trachytic Texture in a Trachyte from Antarctica. The green crystals are Aegirine. PPL image, 2x (Field of view = 7mm)	Trachytic Texture in a Trachyte from Antarctica. The green crystals are Aegirine. PPL image, 10x (Field of view = 2mm)	Trachytic Texture in a Trachyte from Antarctica. The green crystals are Aegirine. PPL image, 10x (Field of view = 2mm)
Trachytic Texture in a Trachyte from Antarctica. The green crystals are Aegirine. PPL image, 10x (Field of view = 2mm)	Trachytic Texture in a Trachyte from Antarctica. The green crystals are Aegirine. PPL image, 10x (Field of view = 2mm)	Trachytic Texture in a Trachyte from Antarctica. The green crystals are Aegirine. PPL image, 10x (Field of view = 2mm)
Trachytic Texture in a Trachyte from Antarctica. The green crystals are Aegirine. PPL image, 10x (Field of view = 2mm)	Trachytic Texture in a Trachyte from Antarctica. The green crystals are Aegirine. PPL image, 10x (Field of view = 2mm)	Trachytic Texture in a Trachyte from Antarctica. The green crystals are Aegirine. PPL image, 10x (Field of view = 2mm)