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.
Tetrahedral phosphate anions may be replaced by other tetrahedral anions such as (SO4)2-, (SiO4)4-, (MnO4)2-, (ASO4)3-, (CrO4)2- and (VO4)3-.

Optical Properties:

• Relief: high
• Color: colorless
• Interference colors: weak interference colors
• cleavage: poor parallel to (001)
• Form: normally forms tiny euhedral prismatic crystals elongated on c, with exagonal basal section and rectangular to acicular prismatic section.

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.

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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Apatite inclusions in Amphibole. lamprophyric dyke, Sardinia, Italy. PPL image, 10x (Field of view = 2mm)
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Apatite inclusions in Amphibole. lamprophyric dyke, Sardinia, Italy. PPL image, 10x (Field of view = 2mm)
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Apatite inclusions in Amphibole. lamprophyric dyke, Sardinia, Italy. PPL image, 10x (Field of view = 2mm)
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Apatite inclusions in Amphibole. lamprophyric dyke, Sardinia, Italy. PPL image, 10x (Field of view = 2mm)
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Apatite inclusions in Amphibole. lamprophyric dyke, Sardinia, Italy. PPL image, 10x (Field of view = 2mm)
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Apatite inclusions in Amphibole. lamprophyric dyke, Sardinia, Italy. PPL image, 10x (Field of view = 2mm)
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Apatite inclusions in Amphibole. PPL image, 2x (Field of view = 7mm)
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Apatite inclusions in Amphibole. XPL image, 2x (Field of view = 7mm)
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Apatite crystal. PPL image, 10x (Field of view = 2mm)
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Basal section of Apatite enclosed in Amphibole in a Lamproite from Posada Asinara (Sardinia). PPL image, 10x (Field of view = 2mm)
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Apatite crystals enclosed in Amphibole in a Lamproite from Posada Asinara (Sardinia). PPL image, 2x (Field of view = 7mm)
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Apatite crystals enclosed in Amphibole in a Lamproite from Posada Asinara (Sardinia). PPL image, 10x (Field of view = 2mm)
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Apatite crystals enclosed in Amphibole in a Lamproite from Posada Asinara (Sardinia). PPL image, 10x (Field of view = 2mm)
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Apatite crystals enclosed in Amphibole in a Lamproite from Posada Asinara (Sardinia). PPL image, 10x (Field of view = 2mm)


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Apatite structure. Blue dotts are F atoms; Ca sites in green and (PO4) groups in azure. From Stephen. A. Nelson