Apatite - Ca5(PO4)2[F, OH, Cl]

Apatite structure is characterized by phosphate oxyanion linked by Ca2+ cations to forma hexagonal frame-work with F- anions lying at the corners of hexagonal cell and coordinated by three Ca2- cations. Composition of the apatite minerals is highly variable and there is a complete solid solution between three end-members, fluoroapatite Ca5(PO4)3F, chloroapatite Ca5(PO4)3Cl and hydroxylapatite Ca5(PO4)OH. The dominant anion (F,Cl,OH) determinate the Apatite variety. Apatite is a very common early-formed accessory mineral in nearly all type of igneous rocks. Apatite is also concentrated by late magmatic segregation, and it appears in granite pegmatite.

Optical Properties:

Form: Tiny euhedral prismatic crystals elongated on c, with exagonal basal section and rectangular to acicular prismatic section.
Relief: High.
Color: Colorless.
Interference Colors: weak.
cleavage: Poor parallel to (001).


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Green apatite crystals in a carbonatite. Siilinjärvi, Finland. From sand atlas.




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
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Pyroxene in basal section (with colorless apatite inclusions) in a xenolith from Vulsini volcano, Italy. PPL image, 2x (Field of view = 7mm)
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Pyroxene in basal section (with colorless apatite inclusions) in a xenolith from Vulsini volcano, Italy. PPL image, 10x (Field of view = 2mm)
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Pyroxene in basal section (with colorless apatite inclusions) in a xenolith from Vulsini volcano, Italy. PPL image, 10x (Field of view = 2mm)
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Calcite, biotite and apatite (I order gray) crystals in a sövite from So Vicente island, Cape Verde. XPL image, 1x (Field of view = 9mm)
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Calcite and apatite (high relief, colorless) crystals in a sövite from So Vicente island, Cape Verde. PPL image, 1x (Field of view = 9mm)
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Calcite and apatite (I order gray) crystals in a sövite from So Vicente island, Cape Verde. XPL image, 1x (Field of view = 9mm)
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Calcite and apatite (I order gray) crystals in a sövite from So Vicente island, Cape Verde. XPL image, 2x (Field of view = 7mm)
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Calcite and apatite (high relief, colorless) crystals in a sövite from So Vicente island, Cape Verde. PPL image, 2x (Field of view = 7mm)
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Calcite and apatite (I order gray) crystals in a sövite from So Vicente island, Cape Verde. XPL image, 2x (Field of view = 7mm)
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Phlogopite (brown), calcite, apatite (high relief, colorless) and magnetite (black) crystals in a carbonatite from Sokli carbonatite complex, Finland. PPL image, 1x (Field of view = 9mm)
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Phlogopite (high birefringence), calcite, apatite (I order gray) and magnetite crystals in a carbonatite from Sokli carbonatite complex, Finland. XPL image, 1x (Field of view = 9mm)
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Phlogopite (brown), calcite, apatite (high relief, colorless) and magnetite (black) crystals in a carbonatite from Sokli carbonatite complex, Finland. PPL image, 1x (Field of view = 9mm)
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Apatite crystals in biotite. PPL image, 2x (Field of view = 7mm)
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Apatite crystals in biotite. PPL image, 2x (Field of view = 7mm)
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Apatite crystals in biotite. PPL image, 2x (Field of view = 7mm)
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Apatite crystals in biotite. PPL image, 2x (Field of view = 7mm)
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Apatite crystals in biotite. PPL image, 2x (Field of view = 7mm)
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Apatite crystals in biotite. PPL image, 2x (Field of view = 7mm)
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Apatite crystals (hexagonal basal section) in augite. PPL image, 10x (Field of view = 2mm)
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Apatite crystals (hexagonal basal section) in augite. PPL image, 10x (Field of view = 2mm)
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Apatite crystals (hexagonal basal section) in augite. PPL image, 10x (Field of view = 2mm)
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Apatite crystals (hexagonal basal section) in augite. PPL image, 10x (Field of view = 2mm)
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Apatite crystals (hexagonal basal section) in augite. PPL image, 10x (Field of view = 2mm)
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Apatite crystals (hexagonal basal section) in augite. XPL image, 10x (Field of view = 2mm)
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Apatite crystals (hexagonal basal section) in augite. PPL image, 10x (Field of view = 2mm)
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Apatite crystals (hexagonal basal section) in augite. PPL image, 10x (Field of view = 2mm)
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Apatite crystals in augite. PPL image, 10x (Field of view = 2mm)
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Apatite crystals in augite. XPL image, 10x (Field of view = 2mm)
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Apatite crystals in augite. PPL image, 10x (Field of view = 2mm)
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Apatite crystals in augite. PPL image, 10x (Field of view = 2mm)