Embayed texture

Phenocrysts, especially quartz and olivine, in some volcanic and high-level intrusive, and volcanic rocks show rounded embayments. The hypotheses for quartz embayments can be grouped into two categories: 1. melt resorption, 2. skeletal or rapid growth. More specifically, the origin of embayed quartz has been interpreted to result from:

i. Resorption of quartz by the melt due to ascending and decompression.
ii. Resorption of quartz due to magma mixing.
iii. Rapid growth due to undercooling, which result in skeletal texture.

Commonly quartz embayments are interpreted as the result of magmatic corrosion (resorption, dissolution) resulting from a change of conditions that cause a previously stable crystal to become unstable with respect to the liquid, and so to begin dissolving, for example, a change in pressure or a change in chemical composition of the melt caused by mixing of magmas. This interpretation is favored where (1) the corners of the crystal are rounded, (2) compositional zoning is truncated by the embayments and (3) the embayments can be related to fractures in the crystal, since solution would tend to begin at fractures where atoms are more loosely bonded than in a crystal without such defects. The interpretation is also favored where new minerals are deposited on the surface of the embayed crystal, as products of the reaction with the melt; in this instance, the embayed crystal can be foreign to the magma or a phenocryst that has reacted in response to changing conditions.

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
Embayed quartz crystal in a rhyolite porphyry, Odenwald, Germany. PPL image , 2x (Field of view = 7mm)	Embayed quartz crystal in a rhyolite porphyry, Odenwald, Germany. XPL image , 2x (Field of view = 7mm)	Embayed quartz crystal in a rhyolite porphyry, Odenwald, Germany. PPL image , 2x (Field of view = 7mm)
Embayed quartz crystal in a rhyolite porphyry, Odenwald, Germany. PPL image , 2x (Field of view = 7mm)	Embayed quartz crystal in a rhyolite porphyry, Odenwald, Germany. XPL image , 2x (Field of view = 7mm)	Embayed quartz crystal in a rhyolite porphyry, Odenwald, Germany. PPL image , 2x (Field of view = 7mm)
Embayed quartz crystal in a rhyolite porphyry, Odenwald, Germany. XPL image , 2x (Field of view = 7mm)	Embayed quartz crystal in a rhyolite porphyry, Odenwald, Germany. PPL image , 2x (Field of view = 7mm)	Embayed quartz crystal in a rhyolite porphyry, Odenwald, Germany. XPL image , 2x (Field of view = 7mm)
Embayed quartz crystal in a rhyolite porphyry, Odenwald, Germany. PPL image , 2x (Field of view = 7mm)	Embayed quartz crystal in a rhyolite porphyry, Odenwald, Germany. PPL image , 2x (Field of view = 7mm)	Embayed quartz crystal in a rhyolite porphyry, Odenwald, Germany. PPL image , 2x (Field of view = 7mm)
Embayed quartz crystal in a rhyolite porphyry, Odenwald, Germany. XPL image , 2x (Field of view = 7mm)	Embayed quartz crystal in a rhyolite porphyry, Odenwald, Germany. PPL image , 2x (Field of view = 7mm)	Embayed quartz crystal in a rhyolite porphyry, Odenwald, Germany. PPL image , 2x (Field of view = 7mm)
Embayed quartz crystal in a rhyolite porphyry, Odenwald, Germany. PPL image , 2x (Field of view = 7mm)	Embayed quartz crystal in a rhyolite porphyry, Odenwald, Germany. PPL image , 2x (Field of view = 7mm)	Embayed quartz crystal in a rhyolite porphyry, Odenwald, Germany. PPL image , 2x (Field of view = 7mm)
Embayed quartz crystal in a rhyolite porphyry, Odenwald, Germany. PPL image , 2x (Field of view = 7mm)	Embayed quartz crystal in a rhyolite porphyry, Odenwald, Germany. PPL image , 2x (Field of view = 7mm)	Embayed quartz crystal in a rhyolite porphyry, Odenwald, Germany. PPL image , 2x (Field of view = 7mm)
Embayed quartz crystal in a rhyolite porphyry, Odenwald, Germany. PPL image , 2x (Field of view = 7mm)	Embayed quartz crystal in a rhyolite porphyry, Odenwald, Germany. PPL image , 2x (Field of view = 7mm)	Embayed quartz crystal in a rhyolite porphyry, Odenwald, Germany. PPL image , 2x (Field of view = 7mm)
Embayed quartz crystal in a rhyolite porphyry, Odenwald, Germany. PPL image , 2x (Field of view = 7mm)	Embayed quartz crystal in a rhyolite porphyry, Odenwald, Germany. XPL image , 2x (Field of view = 7mm)	Embayed quartz crystal in a rhyolite porphyry, Odenwald, Germany. PPL image , 2x (Field of view = 7mm)
Embayed quartz crystal in a rhyolite porphyry, Odenwald, Germany. XPL image , 2x (Field of view = 7mm)	Embayed olivine crystal in a basalt. PPL image , 2x (Field of view = 7mm)	Embayed (zoned) olivine crystal in a basalt. XPL image , 2x (Field of view = 7mm)
Embayed olivine crystal in a basalt. PPL image , 2x (Field of view = 7mm)	Embayed (zoned) olivine crystal in a basalt. XPL image , 2x (Field of view = 7mm)