118 MINERALOGY AND LITHOLOGY. 
the latter species has often a slight angle between its two optic axes. 
Chlorite forms large aggregations which might be termed rocks, and 
besides its occurrence in what would be termed mineral specimens, it is . 
an essential constituent of chlorite schist, diabase, &c. The particular 
species of a chlorite which exists in a chlorite schist is often hard to 
determine, and the more so because more than one species are liable 
to be present together. For example: in some schists there are basal sec- 
tions of chlorite which remain dark between crossed Nicol prisms during 
a whole revolution (hexagonal), while others, in position likewise parallel 
to the cleavage or base, do not remain dark, and are therefore biaxial. 
The name viridite is reserved for those green chloritic products which 
can be referred to no species, which cannot be isolated for examination, 
and in reference to which it only is known that their appearance and 
association indicate them to be chlorites. The chlorites are usually 
dichroic, with the exception of the viridite which acts at times like an 
amorphous substance. 
Besides its occurrence in the rocks, chlorite is found often in radiated 
and foliated aggregations, in cavities and clefts. The process of hydra- 
tion and alteration of basic rocks usually gives rise to the formation of 
more or less chlorite. The following species have been determined in 
our state. 
77. RipipoLirE (Monocuinic) [Mg’ AP Si? O"% + 4H?O}]. 
This is probably the chlorite that is most abundant in the chlorite 
schists. It is also found in the beds of talc and talc schist, and it occurs 
in well formed crystals at Orford. It is bright green in its color, but 
strongly dichroic, being green in the direction of the vertical axis, while 
it is brown or yellow in a transverse direction. This is best observed in 
thin sections under the microscope. In these sections, as a rule, no 
crystalline form can be noted, but all the sections are double-refracting. 
This chlorite occurs in rocks that do not contain large percentages of 
iron, and do contain considerable magnesia. It may be an original 
product, and it may be the result of the alteration of other minerals. 
Between crossed Nicols it gives brilliant interference colors, and is 
usually more or less impure from the presence of magnetite. 
