U. S. Geological Survey Open-File
Report 01-041
A Laboratory Manual for X-Ray Powder
Diffraction
CHLORITE GROUP
The basic structure of chlorites consists of negatively charged mica-like (2:1) layers regularly alternating with positively charged brucite-like (octahedral) sheets (Grim, 1962). Members of the chlorite group include: brunsvigite, chamosite, clinochlore, cookite, diabantite, nimite, pennantite, penninite, ripidolite, sheridanite, and thuringite. The various members are differentiated by the kind and amount of substitutions within the brucite-like layer and the tetrahedral and octahedral positions of the mica-like layer.
The chlorite minerals are common components of low-grade greenschist facies metamorphic rocks, and of igneous rocks as hydrothermal alteration products of ferromanganese minerals (Deer and others, 1975). Chlorites are also common constituents of argillaceous sedimentary rocks where these minerals occur in both detrital and authigenic forms.
Chlorites have their 001 peaks at 14 to 14.4 angstroms, depending on the individual species. Peak positions are unchanged by ion saturation, solvation with ethylene glycol, or heating. However, heat treatments above 500 C alter peak intensities (Barnhisel and Bertsch, 1989; Moore and Reynolds, 1997). Typically, the 001 chlorite peak may increase dramatically and higher-order peaks may be conspicuously weakened. In poly-mineralic samples, chlorites can be distinguished from kaolinite by comparisons of the 3.58 angstrom kaolinite and 3.54 angstrom chlorite peaks, from smectites by the expansion and contraction of the 001 smectite peak after ethylene glycol solvation and heating to 400 C, and from vermiculite by the progressive collapse of the 001 vermiculite peak during heat treatments.
| X-ray powder diffraction patterns of oriented-aggregate mounts showing the effects of standard treatments
on a chlorite: |
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Selected Bibliography for Chlorite Group
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The basic structure of chlorites consists of negatively charged mica-like (2:1) layers regularly alternating with positively charged brucite-like (octahedral) sheets (Grim, 1962). Members of the chlorite group include: brunsvigite, chamosite, clinochlore, cookite, diabantite, nimite, pennantite, penninite, ripidolite, sheridanite, and thuringite. The various members are differentiated by the kind and amount of substitutions within the brucite-like layer and the tetrahedral and octahedral positions of the mica-like layer. 
Chlorites have their 001 peaks at 14 to 14.4 angstroms, depending on the individual species. Peak positions are unchanged by ion saturation, solvation with ethylene glycol, or heating. However, heat treatments above 500 C alter peak intensities (Barnhisel and Bertsch, 1989; Moore and Reynolds, 1997). Typically, the 001 chlorite peak may increase dramatically and higher-order peaks may be conspicuously weakened. In poly-mineralic samples, chlorites can be distinguished from kaolinite by comparisons of the 3.58 angstrom kaolinite and 3.54 angstrom chlorite peaks, from smectites by the expansion and contraction of the 001 smectite peak after ethylene glycol solvation and heating to 400 C, and from vermiculite by the progressive collapse of the 001 vermiculite peak during heat treatments.
