Smith College - Geology 222b - Petrology

Petrographic Data File

Clinozoisite
Property
Value
Comments
Formula

Ca2Al3O(SiO4)(Si2O7)(OH)

Forms a solid solution series with epidote by substituting Al+3 for Fe+3
Crystal System monoclinic; 2/m  
Crystal Habit rounded grains, columnar or radial aggregates Elongate parallel to the b axis
Cleavage {001} perfect Often controls fragment orientation. Can be difficult to observe due to small grain size.
Hardness 7
Specific Gravity 3.3 - 3.4
Color/Pleochroism

pale green to gray in color, transparent to translucent; not pleochroic.

Optic Sign Biaxial (+)  
Birefringence 0.006-0.0011  
2V 14 - 90 Often > 65
Refractive Index

alpha = 1.706 – 1.724
beta = 1.708 – 1.729
gamma = 1.712 – 1.735

Refractive indices and birefringence increase with iron content.
Extinction Extinction angle to trace of cleavage usually between 0 & 25. Sometimes the extinction angle can be as large as 60.
Distinguishing Features

Distinguishable from epidote in thin section by optic sign, lower birefringence, and absence of green color. Clinozoisite presents maximum first order colors under cross-polarized light and is mostly colorless in plain polarized light.

Occurrence

Commonly present in subduction zones and along contacts of Ca-rich and Al-rich rocks.  Where iron is present, epidote will be formed instead. Clinozoisite and epidote are common accessory minerals in regional and contact metamorphic rocks. It can be present in quartzite, slate, chlorite schist, mica schist, gneiss, amphibole, marble, skarn deposits, hornfels, phyllite, and calc-silicate.

References

Nesse, William D., "Introduction to Optical Mineralogy." Oxford University Press: New York, 2000. pp. 295-296

"Clinozoisite: Clinozoisite Mineral Information and Data." Mineralogy Database - Mineral Collecting, Localities, Mineral Photos and Data. Web. 27 Jan. 2011. <http://www.mindat.org/min-1087.html>.

Editors Abby D'Ambrosia ('07), Lilly Dalton ('11)

 
Photomicrograph of a mostly clinozoisite in plane polarized light . Click on the thumbnail to see a larger PPL/XPL rollover image. Under XPL it is the light-bluish gray mineral.
Photomicrograph of clinozoisite in thin section under plane polarized light. Click on the thumbnail to see a larger image. Rollover image with mouse to see image under cross-polarized light.
Photomicrograph of clinozoisite in thin section under plane polarized light. Click on the thumbnail to see the larger image. Rollover image with mouse to see image under cross-polarized light.


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