Chlorite is a general name for several minerals that
are difficult to distinguish by ordinary methods. These
minerals are all apart of the Chlorite Group of minerals.
The chlorites are often, but not always considered a
subset of the larger silicate group, The clays.
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.