Zircon - ZrSiO4

Zircon is a orthosilicate with a structure in which Zr4+ ions lying between SiO4+ tetrahedra, in a complex coordination with four near and four distant O2-. Zircon contain radioactive elements, that commonly breaks down the crystalline structure in a disordered, isotropic glass (metamict zircon). Hf4+ may replace Zr4+ and Fe3+, Y other REE elements, U and Th commonly replace Zr; PO4 and (OH)4 may replace some SiO4 units. Zircon is a very common accessory mineral in a vast type of rocks, from granite to nepheline syenite. When is enclosed in biotite or amphiboles may form a deeply colored halo in the host mineral for crystal structure break down do to radioactive elements.

Optical Properties:
• Color: Colorless
• Relief: High
• Interference colors: Strong third and fourth-order colors
• Cleavage: Rather poor on (010) and (110)
• Form: Tetragonal crystals often enclosed in biotite, it forms elongated crystals, rounded crystals formed by resorption in magmas.



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
aureolametamittica0066(5).jpg

Pleochroic halo around zircon enclosed in biotite. XPL image. 20x (Field of view = 1mm)		 aureolametamittica0066(3).jpg

Pleochroic halo around zircon enclosed in biotite. PPL image. 20x (Field of view = 1mm)		 aureolametamittica0066(2).jpg

Pleochroic halo around zircon enclosed in biotite. XPL image. 20x (Field of view = 1mm)
aureolametamittica0066(4).jpg

Pleochroic halo around zircon enclosed in biotite. PPL image. 20x (Field of view = 1mm)		 aureolametamittica0066(7).jpg

Pleochroic halo around zircon enclosed in biotite. PPL image. 10x (Field of view = 2mm)		 aureolametamittica0066(8).jpg

Pleochroic halo around zircon enclosed in biotite. PPL image. 10x (Field of view = 2mm)
metamittica(2).jpg

Zircon, enclosed in biotite, with pleochroic halo. PPL image, 10x (Field of view = 2mm)		 metamittica(3).jpg

Zircon, enclosed in biotite, with pleochroic halo. PPL image, 10x (Field of view = 2mm)		 metamittica(4).jpg

Zircon, enclosed in biotite, with pleochroic halo. PPL image, 10x (Field of view = 2mm)
metamittica(5).jpg

Zircon, enclosed in biotite, with pleochroic halo. PPL image, 10x (Field of view = 2mm)		 metamittica(6).jpg

Zircon, enclosed in biotite, with pleochroic halo. PPL image, 10x (Field of view = 2mm)		 metamittica(7).jpg

Zircon, enclosed in biotite, with pleochroic halo. PPL image, 10x (Field of view = 2mm)