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 and U and Th commonly replace Zr; PO4 and (OH)4 may replace some SiO4 units.

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.

Zircon is a very common accessory mineral in a vast type of rocks, from granite to nepheline syenite. When is associated with Biotite or Amphiboles may form a deeply colored halo in the host mineral for crystal structure break down do to radioactive elements.

Bibliography



• Deer, W.A., Howie, R.A., Zussman, J. (1998) Rock-forming Minerals.
• Optical Mineralogy : The Nonopaque Minerals by Phillips / Griffen
• E. WM. Heinrich (1956): Microscopic Petrografy. Mcgraw-hill book company,inc


Photo
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Pleochroic halo around zircon enclosed in Biotite. XPL image. 20x (Field of view = 1mm)
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Pleochroic halo around zircon enclosed in Biotite. PPL image. 20x (Field of view = 1mm)
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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)
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Pleochroic halo around zircon enclosed in Biotite. PPL image. 10x (Field of view = 2mm)
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Pleochroic halo around zircon enclosed in Biotite. PPL image. 10x (Field of view = 2mm)
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Zircon, enclosed in Biotite, with pleochroic halo. PPL image, 10x (Field of view = 2mm)
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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)
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Zircon, enclosed in Biotite, with pleochroic halo. PPL image, 10x (Field of view = 2mm)
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Zircon, enclosed in Biotite, with pleochroic halo. PPL image, 10x (Field of view = 2mm)