Fundamental Minerals

Sialic Minerals

Feldspars

Feldspathoids

Quartz

Femic Minerals

Spodumene

Accessory Minerals

Rare Accessory

Alteration Products

Microstructures

Rocks

Jacupiranga complex

Chlorite - (Mg,Fe²⁺,Fe³⁺,Mn,Al)₁₂[(Si,Al)₈O₂₀](OH)₁₆

Chlorite is the group name for about 10 related minerals. However, the term Chlorite can be used both to describe the group in general, or as a specific term to describe any green member of the Chlorite group whose exact identity is not practical to be determined. The Chlorite group minerals are mostly monoclinic (also triclinic or orthorhombic) micaceous phyllosilicate minerals with a structure consisting of T-O-T layers with two layers having their silicate tetrahedral apices pointing towards each other, separated by an interlayer that may be simple octahedrally coordinated cations or which may be a brucite-like layer of two sheets of closely packed OH groups with the interstices between sheets providing the octahedral cordination site. Chlorites can be described by the following four endmembers based on their chemistry via substitution of the following four elements in the silicate lattice:

• Clinochlore: (Mg₅Al)(AlSi₃)O₁₀(OH)₈
• Chamosite: (Fe₅Al)(AlSi₃)O₁₀(OH)₈
• Nimite: (Ni₅Al)(AlSi₃)O₁₀(OH)₈
• Pennantite: (Mn,Al)₆(Si,Al)4O₁₀(OH)₈

In addition, zinc, lithium, and calcium species are known. The great range in composition results in considerable variation in physical, optical, and X-ray properties. Similarly, the range of chemical composition allows chlorite group minerals to exist over a wide range of temperature and pressure conditions. For this reason chlorite minerals are ubiquitous minerals within low and medium temperature metamorphic rocks, some igneous rocks, hydrothermal rocks and deeply buried sediments.

Chlorite is often found with biotite, garnet, staurolite, andalusite, muscovite, chloritoid, and cordierite in pelitic rocks. In mafic rocks, it occurs with talc, serpentine, actinolite, hornblende, epidote, and garnet. It can also be found with feldspars, quartz, calcite, dolomite, olivine, plagioclase, rutile, ilmenite, titanite, magnetite, chromite, sulfides, zircon, and zeolites. Chlorite forms by the alteration of mafic minerals such as pyroxenes, amphiboles, biotite, staurolite, cordierite, garnet, and chloritoid. Chlorite can also occur as a result of hydrothermal alteration of any rock type, where recrystallization of clay minerals or alteration of mafic minerals produce chlorite.

Optical Properties:
• Color: Colourless ore green, pale green
• Habit: Tabular crystals with pseudo-hexagonal shape
• Cleavage: (001) perfect
• Interference colors: Very weak (brown, deep green, gray), usually with anomalous deep berlin blue
• Relief: Low to moderate

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.

biotite replaced by chlorite (green). PPL image, 10x (Field of view = 2mm)	biotite replaced by chlorite (with deep berlin blue Interference colors). XPL image, 10x (Field of view = 2mm)	Radial aggregates of chlorite in a gabbro. XPL image, 10x (Field of view = 2mm)
Radial aggregates of chlorite in a gabbro. XPL image, 10x (Field of view = 2mm)	Radial aggregates of chlorite in a gabbro. XPL image, 10x (Field of view = 2mm)	Radial aggregates of chlorite in a gabbro. XPL image, 10x (Field of view = 2mm)
Radial aggregates of chlorite in a gabbro. XPL image, 10x (Field of view = 2mm)	Radial aggregates of chlorite in a gabbro. XPL image, 10x (Field of view = 2mm)	Radial aggregates of chlorite in a gabbro. XPL image, 10x (Field of view = 2mm)
Radial aggregates of chlorite in a gabbro. PPL image, 10x (Field of view = 2mm)	Radial aggregates of chlorite in a gabbro. XPL image, 10x (Field of view = 2mm)	Radial aggregates of chlorite in a gabbro. XPL image, 10x (Field of view = 2mm)
Radial aggregates of chlorite in a gabbro. XPL image, 10x (Field of view = 2mm)	Radial aggregates of chlorite in a gabbro. XPL image, 10x (Field of view = 2mm)	Radial aggregates of chlorite in a gabbro. XPL image, 10x (Field of view = 2mm)
Biotite partially replaced by chlorite. XPL image, 10x (Field of view = 2mm)	Biotite partially replaced by chlorite. PPL image, 10x (Field of view = 2mm)	Biotite partially replaced by chlorite. XPL image, 10x (Field of view = 2mm)
Biotite partially replaced by chlorite. PPL image, 10x (Field of view = 2mm)	Biotite partially replaced by chlorite. XPL image, 10x (Field of view = 2mm)	Biotite partially replaced by chlorite. XPL image, 10x (Field of view = 2mm)
Biotite replaced by chlorite. PPL image, 10x (Field of view = 2mm)	Biotite partially replaced by chlorite. XPL image, 10x (Field of view = 2mm)	Biotite partially replaced by chlorite. XPL image, 10x (Field of view = 2mm)
biotite replaced by chlorite (Interference colors ranging from blue to green). XPL image, 10x (Field of view = 2mm)	biotite replaced by chlorite (Interference colors ranging from blue to gray). XPL image, 10x (Field of view = 2mm)	biotite replaced by chlorite (Interference colors ranging from blue to green). XPL image, 10x (Field of view = 2mm)
biotite replaced by chlorite (Interference colors ranging from blue to green). XPL image, 10x (Field of view = 2mm)	biotite replaced by chlorite (Interference colors ranging from blue to green). XPL image, 10x (Field of view = 2mm)	biotite replaced by chlorite (Interference colors ranging from blue to green). XPL image, 10x (Field of view = 2mm)
biotite replaced by chlorite (with deep berlin blue Interference colors). XPL image, 2x (Field of view = 7mm)	biotite replaced by chlorite (with deep berlin blue Interference colors). XPL image, 2x (Field of view = 7mm)	biotite replaced by chlorite (with deep berlin blue Interference colors). XPL image, 2x (Field of view = 7mm)
biotite replaced by chlorite (with deep berlin blue Interference colors). XPL image, 2x (Field of view = 7mm)	biotite replaced by chlorite. PPL image, 2x (Field of view = 7mm)	biotite replaced by chlorite. XPL image, 2x (Field of view = 7mm)
biotite crystals replaced by chlorite. Giglio island Granite (Italy). XPL image, 2x (Field of view = 7mm)	biotite crystals replaced by chlorite. Giglio island Granite (Italy). XPL image, 2x (Field of view = 7mm)	biotite crystals replaced by chlorite. Giglio island Granite (Italy). XPL image, 2x (Field of view = 7mm)
biotite replaced by chlorite. Giglio island Granite (Italy). XPL image, 10x (Field of view = 2mm)	biotite replaced by chlorite. Giglio island Granite (Italy). XPL image, 10x (Field of view = 2mm)	biotite replaced by chlorite. Giglio island Granite (Italy). XPL image, 10x (Field of view = 2mm)
biotite replaced by chlorite. Giglio island Granite (Italy). XPL image, 10x (Field of view = 2mm)	biotite replaced by chlorite. Giglio island Granite (Italy). XPL image, 10x (Field of view = 2mm)	biotite replaced by chlorite. Giglio island Granite (Italy). XPL image, 10x (Field of view = 2mm)
biotite replaced by chlorite and Calcite. Giglio island Granite (Italy). XPL image, 10x (Field of view = 2mm)	biotite replaced by chlorite. Giglio island Granite (Italy). XPL image, 10x (Field of view = 2mm)	biotite replaced by chlorite. Giglio island Granite (Italy). XPL image, 10x (Field of view = 2mm)