Sagenitic Biotite

The term "sagenitic texture" refers to the occurrence of slender, needlelike inclusions intersecting at angles of 60° and included in phlogopite, quartz, or other minerals. Although such acicular inclusions have long been thought to consist of rutile, titanite, hematite, tourmaline, zircon, apatite, or allanite. Sagenitic rutile form for exsolution processes in Ti-bearing Biotite as fine needles.

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
Sagenitic Biotite with needlelike inclusions of rutile. PPL image , 10x (Field of view = 2mm)	Sagenitic Biotite with needlelike inclusions of rutile. PPL image , 10x (Field of view = 2mm)	Sagenitic Biotite with needlelike inclusions of rutile. PPL image , 10x (Field of view = 2mm)
Sagenitic Biotite with needlelike inclusions of rutile. PPL image , 20x (Field of view = 1mm)	Sagenitic Biotite with needlelike inclusions of rutile. PPL image , 2x (Field of view = 7mm)	Sagenitic Biotite with needlelike inclusions of rutile. PPL image , 2x (Field of view = 7mm)
Sagenitic Biotite with needlelike inclusions of rutile. PPL image , 20x (Field of view = 1mm)	Sagenitic Biotite with needlelike inclusions of rutile. PPL image , 20x (Field of view = 1mm)	Sagenitic Biotite with needlelike inclusions of rutile. XPL image , 20x (Field of view = 1mm)
Sagenitic Biotite with needlelike inclusions of rutile. PPL image , 10x (Field of view = 2mm)