The general formula for chlorite is (Fe, Mg, Al)6(Si, Al)4O10(OH)8. However there are several different minerals that are apart of the chlorite group of minerals. The above formula is only a generalization of the more common members of this group. In order to see a list of most of the chlorite group minerals with their respective formula, see the discussion of the Chlorite Group.
For practical reasons most of the chlorites will be considered here as a single mineral, chlorite. Chlorites are generally green and crystallize in the monoclinic symmetry system. They all have a basal cleavage due to their stacked structure. Chlorites typically form flaky microscopic crystals and it is this reason that they are sometimes included in the clay group of minerals. However chlorites also form large individual tabular to platy crystals that are unlike most of the other clay minerals.
Chlorites are most often known to mineral collectors as inclusions in or coatings on quartz, danburite, topaz, calcite and many other minerals. The inclusions are usually a very strong green color despite the small amount of material that actually constitutes the inclusion. These inclusions and coatings can be an enhancement but are more often a bane to what might have been a really valuable mineral specimen.
The chlorite inclusions in clear quartz are particularly interesting when they form as a coating on a crystal early in its development. Because if the crystal later grows larger, ie. out and around the chlorite coating, the effect will be to produce a phantomed crystal. A phantom is a crystal that appears to have a smaller crystal inside of it. Many times the interior "crystal" is indistinct or ghostly and thus the name phantom.
There are many minerals that make up the chlorites and thus many varieties. One variety is called kaemmererite and is a variety of the chlorite clinochlore. Sometimes kaemmererite is called chromian clinochlore because of the increase chromium content. It is the chromium that gives kaemmererite its bright lavender to deep crimson red color.