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



• Deer, W.A., Howie, R.A., Zussman, J. (1998) Rock-forming Minerals.
• Nesse, William D., 1986, Introduction to Optical Mineralogy: New York, Oxford University Press




Photo
cccloritee(13).jpg

biotite replaced by chlorite (green). PPL image, 10x (Field of view = 2mm)/td>
cccloritee(2).jpg

biotite replaced by chlorite (with deep berlin blue Interference colors). XPL image, 10x (Field of view = 2mm)/td>
clorite(2).jpg

Radial aggregates of Chlorite in a Gabbro. XPL image, 10x (Field of view = 2mm)/td>
clorite(3).jpg

Radial aggregates of Chlorite in a Gabbro. XPL image, 10x (Field of view = 2mm)/td>
clorite(4).jpg

Radial aggregates of Chlorite in a Gabbro. XPL image, 10x (Field of view = 2mm)/td>
clorite(5).jpg

Radial aggregates of Chlorite in a Gabbro. XPL image, 10x (Field of view = 2mm)/td>
clorite0584(11).jpg

Radial aggregates of Chlorite in a Gabbro. XPL image, 10x (Field of view = 2mm)/td>
clorite0584(12).jpg

Radial aggregates of Chlorite in a Gabbro. XPL image, 10x (Field of view = 2mm)/td>
clorite0584(13).jpg

Radial aggregates of Chlorite in a Gabbro. XPL image, 10x (Field of view = 2mm)/td>
clorite0584(14).jpg

Radial aggregates of Chlorite in a Gabbro. PPL image, 10x (Field of view = 2mm)/td>
clorite0584(15).jpg

Radial aggregates of Chlorite in a Gabbro. XPL image, 10x (Field of view = 2mm)/td>
clorite0584(16).jpg

Radial aggregates of Chlorite in a Gabbro. XPL image, 10x (Field of view = 2mm)/td>
clorite0584(19).jpg

Radial aggregates of Chlorite in a Gabbro. XPL image, 10x (Field of view = 2mm)/td>
clorite0584(20).jpg

Radial aggregates of Chlorite in a Gabbro. XPL image, 10x (Field of view = 2mm)/td>
clorite0584(21).jpg

Radial aggregates of Chlorite in a Gabbro. XPL image, 10x (Field of view = 2mm)/td>
cccloritee(4).jpg

Biotite partially replaced by Chlorite. XPL image, 10x (Field of view = 2mm)/td>
cccloritee(5).jpg

Biotite partially replaced by Chlorite. PPL image, 10x (Field of view = 2mm)/td>
cccloritee(6).jpg

Biotite partially replaced by Chlorite. XPL image, 10x (Field of view = 2mm)/td>
cccloritee(7).jpg

Biotite partially replaced by Chlorite. PPL image, 10x (Field of view = 2mm)/td>
cccloritee(8).jpg

Biotite partially replaced by Chlorite. XPL image, 10x (Field of view = 2mm)/td>
cccloritee(9).jpg

Biotite partially replaced by Chlorite. XPL image, 10x (Field of view = 2mm)/td>
cccloritee(10).jpg

Biotite replaced by Chlorite. PPL image, 10x (Field of view = 2mm)/td>
cccloritee(11).jpg

Biotite partially replaced by Chlorite. XPL image, 10x (Field of view = 2mm)/td>
cccloritee(12).jpg

Biotite partially replaced by Chlorite. XPL image, 10x (Field of view = 2mm)/td>
cloritegrecia(5).jpg

biotite replaced by chlorite (Interference colors ranging from blue to green). XPL image, 10x (Field of view = 2mm)/td>
cloritegrecia(6).jpg

biotite replaced by chlorite (Interference colors ranging from blue to gray). XPL image, 10x (Field of view = 2mm)/td>
cloritegrecia(7).jpg

biotite replaced by chlorite (Interference colors ranging from blue to green). XPL image, 10x (Field of view = 2mm)/td>
cloritegrecia(8).jpg

biotite replaced by chlorite (Interference colors ranging from blue to green). XPL image, 10x (Field of view = 2mm)/td>
cloritegrecia(9).jpg

biotite replaced by chlorite (Interference colors ranging from blue to green). XPL image, 10x (Field of view = 2mm)/td>
cloritegranito2012(2).jpg

biotite replaced by chlorite (Interference colors ranging from blue to green). XPL image, 10x (Field of view = 2mm)/td>
cloritegranito2012(3).jpg

biotite replaced by chlorite (with deep berlin blue Interference colors). XPL image, 2x (Field of view = 7mm)/td>
cloritegranito2012(4).jpg

biotite replaced by chlorite (with deep berlin blue Interference colors). XPL image, 2x (Field of view = 7mm)/td>
cloritegranito2012(5).jpg

biotite replaced by chlorite (with deep berlin blue Interference colors). XPL image, 2x (Field of view = 7mm)/td>
cloritegranito2012(6).jpg

biotite replaced by chlorite (with deep berlin blue Interference colors). XPL image, 2x (Field of view = 7mm)/td>
clorite2013(5).jpg

biotite replaced by chlorite. PPL image, 2x (Field of view = 7mm)/td>
clorite2013(2).jpg

biotite replaced by chlorite. XPL image, 2x (Field of view = 7mm)/td>
cloritegiglio(2).jpg

biotite crystals replaced by chlorite. Giglio island Granite (Italy). XPL image, 2x (Field of view = 7mm)/td>
cloritegiglio(3).jpg

biotite crystals replaced by chlorite. Giglio island Granite (Italy). XPL image, 2x (Field of view = 7mm)/td>
cloritegiglio(4).jpg

biotite crystals replaced by chlorite. Giglio island Granite (Italy). XPL image, 2x (Field of view = 7mm)/td>
cloritegiglio(5).jpg

biotite replaced by chlorite. Giglio island Granite (Italy). XPL image, 10x (Field of view = 2mm)/td>
cloritegiglio(6).jpg

biotite replaced by chlorite. Giglio island Granite (Italy). XPL image, 10x (Field of view = 2mm)/td>
cloritegiglio(7).jpg

biotite replaced by chlorite. Giglio island Granite (Italy). XPL image, 10x (Field of view = 2mm)/td>
cloritegiglio(8).jpg

biotite replaced by chlorite. Giglio island Granite (Italy). XPL image, 10x (Field of view = 2mm)/td>
cloritegiglio(9).jpg

biotite replaced by chlorite. Giglio island Granite (Italy). XPL image, 10x (Field of view = 2mm)/td>
cloritegiglio(10).jpg

biotite replaced by chlorite. Giglio island Granite (Italy). XPL image, 10x (Field of view = 2mm)/td>
cloritegiglio(11).jpg

biotite replaced by chlorite and Calcite. Giglio island Granite (Italy). XPL image, 10x (Field of view = 2mm)/td>
cloritegiglio(13).jpg

biotite replaced by chlorite. Giglio island Granite (Italy). XPL image, 10x (Field of view = 2mm)/td>
cloritegiglio(14).jpg

biotite replaced by chlorite. Giglio island Granite (Italy). XPL image, 10x (Field of view = 2mm)/td>