Apatite - Ca₅(PO₄)₂[F, OH, Cl]

Apatite was named apatite by the German geologist Abraham Gottlob Werner in 1786. Apatite is often mistaken for other minerals. This tendency is reflected in the mineral's name, which is derived from the Greek word (apatein), which means to deceive or to be misleadin. Apatite is a group of phosphate minerals, usually referring to hydroxyapatite, fluorapatite and chlorapatite, with high concentrations of OH^-, F^- and Cl^- ions.

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 Ca^2- 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. 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-.

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:

• 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.

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
Apatite inclusions in amphibole. Lamprophyric dyke, Sardinia, Italy. PPL image, 10x (Field of view = 2mm)	Apatite inclusions in amphibole. Lamprophyric dyke, Sardinia, Italy. PPL image, 10x (Field of view = 2mm)	Apatite inclusions in amphibole. Lamprophyric dyke, Sardinia, Italy. PPL image, 10x (Field of view = 2mm)
Apatite inclusions in amphibole. Lamprophyric dyke, Sardinia, Italy. PPL image, 10x (Field of view = 2mm)	Apatite inclusions in amphibole. Lamprophyric dyke, Sardinia, Italy. PPL image, 10x (Field of view = 2mm)	Apatite inclusions in amphibole. Lamprophyric dyke, Sardinia, Italy. PPL image, 10x (Field of view = 2mm)
Apatite inclusions in amphibole. Lamprophyric dyke, Sardinia, Italy. PPL image, 2x (Field of view = 7mm)	Apatite inclusions in amphibole. Lamprophyric dyke, Sardinia, Italy. XPL image, 2x (Field of view = 7mm)	Apatite crystal. Lamprophyric dyke, Sardinia, Italy. PPL image, 10x (Field of view = 2mm)
Basal section of apatite enclosed in amphibole. Lamprophyric dyke, Sardinia, Italy. PPL image, 10x (Field of view = 2mm)	Apatite crystals enclosed in amphibole. Lamprophyric dyke, Sardinia, Italy. PPL image, 2x (Field of view = 7mm)	Apatite crystals enclosed in amphibole. Lamprophyric dyke, Sardinia, Italy. PPL image, 10x (Field of view = 2mm)
Apatite crystals enclosed in amphibole. Lamprophyric dyke, Sardinia, Italy. PPL image, 10x (Field of view = 2mm)	Apatite crystals enclosed in amphibole. Lamprophyric dyke, Sardinia, Italy. PPL image, 10x (Field of view = 2mm)